TheMonkofDestiny: This is a question only Bethesda could answer. I would say you're just as likely to get a response by emailing them directly about it than you are here in this thread.

Having said that, I would not expect the full version of the game to come to GOG, provided that it ever does at all at some point in the future.

I strongly suspect that the multiplayer (and subsequent multiplayer-centric DLCs you mentioned) and the SnapMap functionality will be ripped out of it entirely because Bethesda won't support either through a separate GOG release. And while this may not be an issue for some, given that the game's multiplayer was kind of a dud anyway and even id decided that the world would be better off without more SnapMap when the time came for Doom Eternal, there will still be a few people upset by the loss of features to the game.