I'm more than ready to give the $100 greelight fees to someone making the plug-in.
I already have 2 games of mine on Steam, but we made it with a publisher, and most important as a team. Now will be the first time I'm making a steam targeted game alone, and I will have to pay a "real" coder to implement steamworks anyway on the top of my game.
So, it worth the money to have a plug-in for everyone and not only for me.
I like the idea to see C2 as a real engine, and not only for hobbyists. GameMaker has Steam support, and C2 is at least as great to develep with, I don't see why someone would not like to get this feature :)