Hah thanks for the find ma I remember this post, but had no idea where to look for it.
IMO, the steam implementation shouldn't be a problem, because there are quite few games which aren't/weren't implemented for steam at all. Eg. Dark Souls 1, used to work with GFWL[1] (hugest deepest excrement ever ^^), but it was still possible to buy the game over steam, activate it and use it there, without using GFWL to launch it. Like a week ago GFWL got removed and DS1 got implemented for steam ALONG with achievements. I am not sure how exactly it works, but i guess it might be possible to refuse implementing the game for steam in any way. But that would require someone who actually knows something more about this than speculations.
The main problem i see right now, is the lack of updates. I am not sure how nicely would steam look at a game, which wasn't updated in few months (half a year? A year?). Even tho pretty huge pro would be, that the game stayed active/alive for few years now. That's not an issue people come to greenlight with, they come there to get someone to keep the game alive/active, not to get more active people i think.
[1]GFWL - Games for Windows Live, an attempt to create steam-like launcher from microsoft, which was a complete failure (the facts might have been affected by the hate on GFWL)
