I have tried quickly to install with Wine but I got a an error and didn't try further because I have Windows too.
The problem I see with adding the Linux version as a bonus is that people will ask the same for every game and it could become complicated.
Well, I don't see where offering that on games that already have Linux versions would be that big a hassle, probably just a request to the devs. Games that don't have an existing Linux version aren't going to get one here, simply because GOG can't be expected to write an entirely new version of a game, and how many of the guys there know Wine well enough to make wrappers for each game? I don't know about anyone else, but I'd like to think I'm a pretty reasonable person.
That said, yeah, I have Windows too. We're not at the point where a gamer can just have Linux, and I doubt we will ever reach that point.