I think Endless Space 2 should follow more Endless Legends ai behavior in diplomacy where Alliances can actually fragment.

Right now you make an alliance and it will last to the end or until you the player ends it, to cheap out an easy victory (Another issue that needs to be fixed)

I think the game could benefit from more diplomatic shifts, ai breaking off alliances, betrayals like pretending to be at peace to then declaring war after they move their fleets into position