Good! That probably won't make it work seamlessly on SteamOS, but it's a step forward.
SteamOS is so locked down that they don't even have Debian's default repositories installed by default. In order for GOG games to work with SteamOS (and I mean truly work and not just manually adding them yourself the way you'd do if you were using Ubuntu) CDPR and Valve would have to reach an agreement to tack on a GOG interface to SteamOS and that probably won't happen for a long time just because, if for no other reason, they are still trying to get SteamOS fully functional and reasonably stable and can't add more potentially destabilizing features.
Oh and also who the f*** wants to build a product that helps their largest competitor sell more product?
Didn't know Valve and GoG were competitors.
Aside of GoG games being drm-free, they cather to different publics. With GoG mostly going for old-school gamers, gamers who want to try old-school PC games and people who want to play The Witcher or any RPG without going on Steam.