I'm going to end up trying this. And as some others have said, with some of these projects and some of the stupid nature of these companies, it may benefit them just to wait to at least it's feature complete and not a bug riddled mess even if not finished.
You got to hate these companies for punishing people which probably own the game. How many millions of copies have they sold on people just double dipping. I'm one of them.
Now you can definitely analyze everything on a project by project basis but certain things, especially if they're designed for owning the game, I'm not sure why I punish the gamers.
For example, this may sound minor, but you could require people to own the steam copy of both games. And install them in the same folder or drive to ensure compatibility. So if you have multiple drives, as long as you have them on your d, e, f, etc drive, there should be no issue. Something where almost the same folder structure of steam and the steam apps common folder is required.
I'm going to end up finding this and trying it out because it sounds really cool.