So now the war has been raging for ten years and the defenses are getting so thick that the war is going to stagnate. Fleets will get chewed to shreds by capable defensive opponents. A few systems will trade hands but the lines will stabilize. So where do we go from here. More defenses, copying of technology from each other?
I think the next expansion should include espionage, getting planets without having to use a fleet. Piracy will no longer pay as the areas thicken with defenses and they will probably hire out as mecenaries to support fleet operations.
The stalemate will continue until the races build giant motherships. You need an entire empire to build one, but it will let you crash through fixed defenses, and break the stalemate. Ships so massive that the capital ships just hang in it shadows.
My few ideas for the races:
Motherships should require systems dedicated to building motherships. They should have to have all the shipyards, supply yards, and at least 4-5 constructors in the gravity well. This would limit which planets can build them and make taking the necesaary planets important. Although the TEC mother ship should be easier to construct than the other races.
Their abilities should reflect an extension of abilities they already have:
TEC should get an ability similar to their area effect missile attack that encompases the whole grav well. Thier mothership should also allow the construction of ships where ever it is and faster if it is in its own gravwell. They should get a massive nuclear strike on any planet they hover over.
Advent mothership should be able to carry a fighter swarm as well as bolster its fighter and repair any losses instantly once per battle. They should also get an upgrade to their capital ship's main gun that allows them to remove entire planets from the game, leaving only asteroids in the wake. I would recommend that the races get shields that would mitigate this effect on planets, at least till the shield generators are destroyed.
Vasari should get an upgrade to their colony ships ability to extract resources. The mothership would strip the entire planet and leave a molten planet in its wake. The vasari need some more improvements to their colonizing ability of red planets so they get a bigger pop boost than they currently have. Also the mothership should be able to warp itself to any plnet in the solar system with any frigates in its immediate area. It should then be able to shunt all it power into opening a gate to allow fllets to follow it. This would eliminate its weapons till the gate shuts down.
I know this is probably wishful thinking but I hope they continue with expansions for a while to come.