Linear RPGs and open-world RPGs are not the same.
Linear RPGs allow the player to chew on things for as long as they like, then poke the sleepy plot into delivering the next big chunk of content. This has a lot of pros and cons.
From the dev's perspective, the pros are powerful. Since the content is gated and carefully scripted, the dev knows exactly who the player is playing, exactly who is in their party, exactly how strong they are, exactly where the plot is, exactly what they've seen and haven't seen. No matter how long the player spends on the Shining Plains, they can't buy anything better than a cutlass and a fireball spell.
In addition, the player has a very crisp trigger. They know how to poke the plot into action: fight the boss, cross the monster bridge, say "I'm ready" to the queen. This action is always very obvious and voluntary, and the player will trigger it when they are ready to experience the next content chunk.
These two things combined allow the devs to make sweeping content chunks. When you cross the monster bridge or fight the boss, things change. There's cutscenes. You're fighting your way out of a dungeon. One of your party members leaves, another one arrives. The world is blown up and there's no way back to where you started...
It can be precise and moving, because you know exactly what the player is doing and who they have with them. It can be big and bombastic because the player explicitly volunteered to go through it.
Open-world RPGs don't have these advantages, because the majority of the world is already available from the start. A player moving from point A to point C isn't really "volunteering" to experience a big plot event at point B. Hell, you don't even know who they are or who's in their party, not when you're creating the content.
Because of this, open-world RPGs typically have hundreds of tiny threads of content instead of large content drops. They also adapt the combat challenges by level-scaling.
Both of these leave the experience bland and featureless in comparison to a linear RPG with its more nuanced challenge curve and bombastic, personalized plot events.
Linear RPGs have downsides, too. The big, obvious one is that their appeal is limited. If you don't like the shoes you're stuck in or the way the plot is going, well, that's too bad. If you want to start over, you'll have to go back through the same shit again, there's no fast way to move through those chapters aside from being more efficient with grinding.
There have been open-world CRPGs since before "CRPG" was a term, but they only came into their own when computers became strong enough to convincingly render the world and its responses to you. This became a more reliable method of drawing the player in than the limited appeal of a carefully-written linear storyline.
Big, splashy, personalized stories were left on the cutting room floor... but I think it's a mistake to assume they're gone for good. Not only is there power in the stories they tell, there's power in the fundamental pacing of a linear RPG. The way the content unfolds is really strong.
What if we could come up with a new RPG subgenre that keeps that power but adopts the freedoms of an open-world approach?
I call it "nonlinear" RPGs.
Imagine if we were going to write Mass Effect as a nonlinear RPG instead of a linear one. The characters and stories would feel the same, but they would silently adapt to the player's choices. Not just "paragon vs renegade": wildly veering so that even the basic setups could be avoided or inverted. Maybe you play a smooth talker with a good record, and you convince the council to take immediate action against the Reapers and the traitorous Spectre. Maybe you play Han Solo, and just buy a crappy ship on your own and fly off to have carefree space adventures.
If it was an open-world game, these would be viable. You have that level of variability in the recent Fallouts, for example. But Fallout doesn't have the heavy "WHAM chew chew chew WHAM" feel of a linear RPG - it's more like wading through vanilla pudding.
In order to make stories adapt to your choices, you have to write variations for every choice the player can make. If you have one big story (like a linear RPG), the cost spirals out of control very quickly. So open-world RPGs use lots of tiny, independent stories. It gives the player feedback and tells them the game accepts the way they're playing their character, but because they're small and have so little effect on the game world, you can write their variants cheaply.
Fortunately, linear RPGs don't need that responsiveness nearly as much. The linear RPG already knows how you're playing your character: they provided it.
But... that's where we need to go to find the kernel of what comes next.
If we want a linear RPG to let the player play a wide variety of characters in a wide variety of ways, we need to have the game respond to those variations.
A linear RPG's "gateways" are always crystal clear. A boss. A bridge. A queen's speech. The player trips them whenever they decide they want to, and the game moves forward.
It's easy to create random events. It's even easy to chain them and thread them so you have repeating villains or escalating challenges. It's easy to make random maps and random subquests. (There, I just cut twenty pages from this essay.)
But what isn't easy is to make the experiences adapt to the player's choices and hit hard without being annoying.
Killing off a character or blowing up a place or putting you in a long dungeon sequence is really, really annoying if it isn't done well. It's not about build-up or epicness: it's about suitability.
In a linear RPG, the characters and places and factions all exist to tell a story. Each one represents a major arc or a piece of an arc in the fundamental pattern of the game.
In Mass Effect, Tali's character represents the attempt to take back your future from the mistakes of your parents. Garrus represents the failings of The System to deal with things, and the lure to work outside it. Wrex represents the struggle to provide a future for people that actively seem to not want one. And Liara represents blue nerd ladies that want to have sex with you.
OK, not every character is equally interesting, but they all have arcs that thread through the games and give you a gateway into the beating heart of the story line. The planets, too, represent tiny pieces of those arcs, allowing the arcs to exist in the game world concretely, instead of as a talking head. Factions like the Spectres and the Council also push the plot arcs along in a powerful, immersive way and create a multi-planet threat to hook things together.
And this is our method.
We aren't generating storylines. We are generating random content, sure, but it's anchored into the characters, factions, and scripted plot events that are the best our universe has to offer. Our random content offers a foundation, a stage for those core ideas to dance on.
One of the issues of open-world games is that the player can choose to be anyone, and it's very hard for the game to figure out what the player's self-image is. Thus the frolicking, daisy-picking assassins in Elder Scrolls games. The game tries to guess which plot arcs will be interesting to you by placing them in places those kinds of characters are likely to go.
But our games have a party, and our party members embody specific plot arcs.
If I'm interested in how the system fails us and what happens when we work outside it, I take Garrus. If I'm interested in the fate of the ancients, I take Liara. If I'm interested in struggling to build a future for people that don't want your help, I take Wrex. Not as a conscious choice, but because I am drawn to their characters right from the start.
Of course, the party structure of existing Mass Effect games wouldn't work, since you basically have everyone all the time and nobody ever leaves or comes back.
It's easy enough to replace that structure with one where the player only has a crew of three or four, and they frequently leave to go on some arc-related personal mission you can't help with. (Of course, you'll meet up with them later when the next piece of the arc comes around...)
This means our arcs have to be written with a bit of flexibility. While the core arc has a specific chain of events (for example, Mordin's plot involves rescuing a research victim, helping her, then distributing a fix), it should also contain a number of background events suitable for A) seeing Mordin repeatedly and getting to know him even if you don't trigger his join event, B) filling out random content with evocative situations (his commenting on the evil bug monsters, for example), and C) Mordin's background work after he's joined and then left and then is kicking around waiting to join again.
With these elements in place, the player would "naturally" be attracted to the local NPCs that seem the most interesting. Which will, of course, be arc characters suitable for adding to the party. Once the party is filled up (with maybe one spare), the others are too busy with their personal situation to join your team right now.
Don't choose to take Liara? Well, Liara will also show up in other space stations or on other planets, chatting about how she's chasing down a new lead on an old ruin. She may even have a small sidequest for you. And, if any of your party members leave for a while, you'll suddenly find she's pretty easy to recruit!
Now that your party is known, the next time you trigger a major content burp (fly to a contested star system, argue with the council, defeat a boss, etc) it'll be laced with the next arc events for your party of characters.
Not tiny drips and drabs, either: the next content batch is a big, bombastic event. A whole new set of planets, characters leaving and arriving, crashing your ship and fighting through a jungle...
This is also easy to mod. You can introduce additional characters with their own arcs pretty easily. Although the character arcs don't really overlap, they do exist in the same space: Mordin's arc introduces a mad science lab where genetic monsters are running amok, but it's inside a planet dedicated to Tali's next big arc element, where she's investigating the whole planet for suitability as a home world. Other elements are also laced in. Some are minor arc elements, some are completely random, but all can be laced together using a simple keyword system and a bunch of NPCs or audio tapes referring to other places. Those can easily be generated randomly.
Right now, we think of RPGs as either a world to play in or as monolithic stories. Instead, we might think of them as a bunch of opportunistic stories that piggyback on characters, factions, and places to assemble their setpieces.
... anyway, I cut about fifteen pages out of this long-ass essay. Hopefully it's not too hard to read.