if there's something i'd like to see in a space 4x is dynamic borders and skirmished without war declaration. civ4 has the former, but i'd like to see something more dramatic, and asking for the moon i'd like to be able to move them through diplomacy. endless legend tried the latter: when there isn't a peace treaty you're free to attack other units in neutral regions and in your own, and in this case the ai won't even get angry. what we have now are fixed borders set in stone which won't move ever. you'll never claim property of a system because you have huge colonies nearby. i want the means to fight for the annexion of macau, or its indipendence, depending which side i'm on.
of the map in stellaris was fluid, now it's exactly like any other paradox game.
It is important to note that for hard and solid borders to exists they must be accepted by all parts with influence in the area, so for a system like that to exist borders should not emanate from some abstract values like influence, population, etc but from diplomatic negotiations, endless SPACE's idea of starting in cold war could actually be a good foundation for that system if peace treaties included the negotiation of mutually recognized territories, in that regarf close inhabited planets, military bases, military presence and economic activities could be all meshed together into an score system so that some system are cheaper to claim than others.