IAmSinistar: If GOG exercises good quality control and the VNs have enough gameplay, then I don't see any reason why they couldn't be added to the catalogue.
Depends what kind of gameplay you're expecting as by definition the most gameplay a pure visual novel can have is branching storyline (and kinetic visual novels don't have even that, they are
novels after all. Obviously there are (plenty of) hybrids that combine visual novel story telling style with gameplay from another genre.
And I definately would want to see VNs on GOG, both original Japanese and Western copycats. Some quality controll will be needed thought, as there's plenty of crap VNs out there (but that can be said about all game genres) and pricing is bit of a problem from GOG.com point of view as VNs tend to be overpriced due to size of their (perceived) audience (and due to japanese VNs tending to be fully narrated by professional voice actors).
Anyone wanting to try some free (fan made) VNs should check
Ren'Py games list. There's over 600 (of various quality) to pick from.