You mentioned SGX & ACD. Are you saying these would be required, or are you talking bi-compatible, where when placed in an SGX with an ACD, you get enhancements? If it's exclusively SGX & ACD, that will ofcoarse drastically limit the number of Turbob's that would be able to play it, which maybe effect sales, though, if anyone's like me, I'd buy it anyways to support the Turbo scene in general.
Doing this on a professional level I deffinitely say requires hard deadlines, or vice versa, they go hand in hand. When we're doing games in our spare time, it's waaaay too easy for RL to step in & slow or stop everything. Obviously RL can still step in when doing it as a full time job, but I'd say much less likely, since you don't have the usual 10hr a day etc. job eating up the time besides the coding.
Speaking of which, have you done some really long coding sessions? I know for me, I personally don't think I could handle doing music for a game exclusively. I sometimes get stuck on a tune, & have to litterally stop & not work on it for a day, or 2, or 3, or etc. Then BAM, I can have a great idea that drives me forward. Something like that would get in the way of a deadline, though, since I've never done music on a daily work schedule, I can't say for 100% certainty that I couldn't. If you're uncertain, maybe there's a way you can do some test runs of 10 hrs of coding, though, I'd make it count. Build something either for your game, or some sort of mini game(an old arcade or atari game?), or something that the dev community in general, & make sure what you're coding is interesting to you in general.
As for the deadline itself, I say get all your ideas together now, before a deadline is set. You mentioned how people can lose steam, & I can say from my own experience that that's VERY true. I personally keep going with my projects, but I do find that when I see more work from the others in our various projects, it does give me a boost, & I assume when I show off a song, or even a partial song, or even a neat idea, that it can atleast give the others a goose of sorts!
I feel like there was another thought or 2 I wanted to convey, but it's slipped my mind, so far now, this is all I can think of, other then GO GO GO Tom/Mal/Bonknuts/etc. Whether you choose to do it in 3 months, or not, I look foward to it!