I was thinking about this today, towards endgame, there is almost no neutral territory in between factions. Every planet is colonized in a system and excluding the sun which noone fights in (haven't figured out why the AI is so afraid of fighting in the star's gravwell) you are either in friendly territory or enemy territory (which is usually heavily fortified on one side).

Why not make more uncolonizable gravwells other than the star, I dunno, black holes or something (unrealistic for a solar system but then the devs said realism has no place in games). This way you can actually raid a known trade route, or have a multiple sided fleet engagement with no static defenses giving one side an edge. Maybe even make them somewhat strategically important somehow.