The 4X genre is incredibly stagnant, and nowhere is that clearer than in the complete failure to offer any kind of political gameplay.
This means that the 4X games are always going to have that fourth X: "Exterminate". If you can't really build a relationship with other nations, you don't have any choice.
There have always been vague, hamhanded concessions to those of us that like "pacifist" gameplay, such as cultural victories or voting for yourself in the galactic senate, but these are very passive experiences that don't feel as strong as the warfare gameplay.
There's no reason for that. Let's do a very easy experiment: let's re-engineer Stellaris so it has political gameplay.
And by "re-engineer" I mean "a mod".
Stellaris is a very flawed game, largely because they tried to extend the midgame but didn't add in much midgame play. We can fix that by adding in politics, and it doesn't require much of a change at all.
First, let's get rid of the "trade" system. We're replacing that with a new way of gaining favor and benefiting from other nations. Instead of trade agreements, we should instead have outreach activities - they fill the same spot and work in the same way, but there are a few differences.
(This makes more sense to me anyway, since individual diplomats would handle details.)
One is that activities have an in-world color. Rather than donating 200 energy, you spend 200 energy hosting a Glarthian history exhibit on your homeworld for ten years. Or you spend it on Glarthian refugees. Or you spend it on raising patrols on the border, creating a trickle of material input due to seized smuggling goods.
The Glarthians will respond in a way that makes sense to their culture, which means different activities will result in different things from different cultures.
The best thing about this approach is that the activities can adapt to the current relationship. The treaties can still exist: if you close your borders, certain things become impossible and others become possible. If you're in a defensive pact, more things are possible and some of the "getting to know you" ones are scrapped. Even during an outright war, you'll still have political actions you take take: to lay the groundwork for peace, to exploit their weaknesses, to perform spy actions.
It's outside of the realm of a mod, but it'd also be pretty easy to set up N-way activities by simply allowing you to invite people to help you do the activity. Whether it's hosting a Glarthian history month or setting up an economy-shredding blockade, just invite anyone you want.
Since Stellaris has colonies that are very building-centric, let's introduce some political buildings. Museums, market districts, embassies. We can even put them on space stations!
Some of these are multi-purpose. Market districts give a steady flow of materials, while museums decrease cultural drift (already a thing in Stellaris). But they also affect the relationship between your nation and any nation whose border is within N light years of the installation.
Rather than trying to get a +1 trust per month by randomly spraying them with credits, how about we use these buildings? Because colonies have limited space, this produces some wonderful new tradeoffs. Right now, having a colony crammed against a few borders is a panic-inducing state of affairs, but how about if you dedicate that colony to international politics? Now it's establishing good relations between you and them, reducing or even reversing the penalty for having borders touching.
Since the colonies are inhabited by populations with explicit values and traits, we can make those buildings modify the populations on the affected worlds. Xenophilic groups will tend to pop up, and if possible, we could add species-specific xenophilia as the people on the planet learn to love Glarthians specifically.
We can even have the various facilities push different traits. Embassies might create pacifism, while museums might create xenophilia (if near a border) or xenophobia (if not near a border).
This would let us take advantage of the already-existing population engine, and a clever person could seed xenophilia throughout a neighboring nation, then use outreach activities to put those populations in power and change the nature of their empire.
Now imagine if that xenophilia was specific to your species! Or imagine it was pacifism, and you've changed a warlike nation! There's a lot of potential to let the player customize their approach.
While it'd be tough to mod it into Stellaris, it'd be fun to have some control over the pro-you factions in other nations. Right now there is a faction control system in Stellaris, why not have foreign factions that you have some control over in that list?
One thing that's easy to overlook is that the Enterprise was always as much a political vessel as a science vessel. Why don't we add a few new science ship components?
Specifically, political/outreach facilities. You can research and upgrade them just like sensor kits.
Ships with political facilities will automatically improve relationships with whoever they are orbiting. As long as you have open borders, you can use your science ships to wage peace.
We could have the facilities mirror our colony facilities, allowing us to create traits such as xenophilia or a physics specialty or pacifism on the planets we orbit, instead of at random. Moreover, this would mean we could park our science ships over our own planets to mold our own populations in that way.
Although it'd be hard to mod it into Stellaris, it'd be nice to have another category of science mission: political outreach missions. These might pop up at random, or maybe you have to survey worlds again every few years to have a chance of uncovering one. The science ships with outreach modules can perform these outreach missions and things will go better between your people and theirs.
There's also how to counteract these cultural attacks. Even closing your borders doesn't completely prevent them. So why not have some more policies, facilities, or science ship components that specifically negate the effect of museums or science ships, preventing your people from developing traits you don't like.
And, of course, you can take political stances that force them to back off - cultural preservation or something.
There's a lot of potential here, and it's so close to being something we could simply mod into Stellaris.
So... why are 4X games so stagnant? Look at all this stuff we could be doing with it!