This is supposed to be a listing of things that are in GC2, that can be improved, but would probably require more engine work then is feasible, and therefore would need to wait until GC3.
1) Governments.
I'd like to see each race have a different set of government techs, and be unique in that regard. This is not doable in GC2 I think.
2) Super Abilities
I'd like to see the abilities transformed from magical special abilities- into techs that are unique and can be learned. This one may be doable in GC2, but it won't happen- GC3 could take the GC2 concepts and increase the efficiency by coding them in a new way.
3) Events
My biggest annoyance. I'd like to see events expanded- have triggers based on political party, relations, etc. Throw some common sense into it- a War Party may trigger wars, a Populist party might anger aliens, a Federalist party might have internal issues, a Technologist party might have research chances/really bad things happen, etc...
Some events might also give a chance to change political party. Events should have more, and possibly unforseen consequences
4) Xeno Ethics
I'd really like to see this branch of the tree abolished or transformed. It doesn't make a lot of sense, except to get benefits from an alignment. I think it should be changed to make events more beneficial to a chosen alignment- the knowledge of how to exploit your social values.
5) Anomalies
The current system is a complete relic from GC1 and should be changed. It's likely doable now but forgotten about
6) Constructors
Late game, a single constructor just isn't enough. There needs to be a way to put multiple constructor modules on a hull. Also, constructor modules should be upgradeable.
7) Diplomacy/Tech Trading
The AI needs to value goods and techs more realistically. I know this would take a big chunk of AI resources. I wouldn't mind turns being split into diplo and manuever turns if needed to help the AI out with this. Also, Economic and Research treaties need more effective events.
8) Economics.
I'd like to see a diminishing marginal return effect on excess factories/labs/markets on a planet. This would be put into an efficiency rating. The efficiency rating would also be modified by population- more population increases efficiency- as you'd have more geniuses better suited to work. Each race would have different efficiency. Yor, being machines, would have less of a problem then say Terrans, while Arceans might have a massive problem in some areas. Co-ordination centers and power plants would help counter the effects some as well.
There you go- 8 concepts I think I'd like to see in GC3, should they decide to evolve GC2 for it, which is mostly what I'd want- as I think GC2 idea well won't be run dry by TA. There's still work that should be done, even after TA- though it may require a new game.
(This is how I feel about most really excellent games though)