I started out being quite picky as I had only 8, and ended with 5...
- Strategic overlay. I am not sure what this is, but any bigger picture view would be nice. The map can be messy once you are quite big. 10 fleets, 80 single frigates/escorts, a lots of long range scanners (with long ranges), a few deep cover spies. It gets messy :)
- Improved research mechanic. Bases are build and forget today. And the AI is not so good at building fast enough.
- Exploration ship options. They are stupid, and you want to tell them what to focus on. The thing here is that the AI needs to know what to do early as well...
- Galactic news service. Very much so! But don't make the bug where you get new involving empires you have not yet met...
- More tech tree components. Not so much specific new stuff, but I feel the trees may have good of some work to make picking stuff harder. The weapon tree is too simple to choose from for me.
- Bigger galaxy map. I want distances! More fuel issues, not less.
- Conquer/colonise. How about empire policies on migrants? I settle on korabbia, with 20m population max, and the population is swapped all the time. I want only Dhayut here, dammit! How about forcing migration. "All Kiadians are expelled from the empire". The dark blues may not be too happy about that...
- More diplomacy. I want to make all kinds of nifty ultimatums. And more.
No, I did not forget about firing arcs, leaders, ground combat, ship boarding, I very much went past them.