Garry said it would go through Greenlight if he wanted it on Steam, even though he could probably strike a deal with Valve. That's about it. I don't think it's much of a concern right now.
Quote from Garry's blog:
http://garry.tv/ posted:
With the Steam stuff – I think we’re going to go through the greenlight system. This is for two reasons. First of all I’d feel kinda like I was stepping on all the other people on greenlight if we went around it, and second of all – if it doesn’t get greenlit then it shouldn’t be on Steam in the first place.
http://garry.tv/
You guys should learn to use Google (or first and foremost read the sticky), it'd make 90% of the threads here redundant. Anyway, chances are Garry will announce plans and such on his blog anyway, watch that instead of clogging up the forums.