One suggestion I already thought of while tinkering with the 2.2 demo and watching the video of v3 was I'd like to see you retain the ability to simplify the graphics down to the bare minimum so it can just all out run as fast as possible. In fact, I'd love just having one button for switching back and fourth between the chosen high quality settings, and bare minimum settings.
Not that I don't love eye candy, but I wanted to do simulations over extended periods of time, if anything just to see how the system drifts, and how long it takes to reach a point of orbital resonances, if ever. It would probably take a lot of days of processing for that, at least with v2.2. On v2.2 I estimated a 20 body system would get maybe 3,000 years per day of processing with graphics at the minimum (full screen goes faster I noticed) and accuracy at near maximum. Perhaps it's partially because v2.2 only really utilizes one of my cores, and the others only bit. idk
Anyways, since it sounds like you're fairly close to releasing v3, I think I shall just wait and buy it.