So, I've started scratching the surface of EU IV, after around 200 hours of Stellaris (after which I am still terrible), I found that Claims could honestly do wonders for both diplomacy and war in Stellaris. What got me thinking about this is the fact that you already know the entire border regions of an empire when you meet. I don't feel like it makes sense for you to know that information, or for you to give it freely (and another thing, the border stations... Can't recall the name). If anything, I think that only the system you found should be revealed as being their "territory", out better yet, that their territory extends to just their colonized systems, with the surrounding systems simply being claims. Adding in the ability to dispute their claim on an area would be good as well, maybe with your power in that area being influenced by how legitimate your claim is (this system is closer to X's Unity colony, but the Y still consider it as their system. Both can build in the area, but it would require influence to do). Ship maintenance might also be affected by claims? Idk.
Really, I'm just rambling, but I feel like it might be able to improve the game in some ways.
Really, I'm just rambling, but I feel like it might be able to improve the game in some ways.