tudhalyas: I see two main reasons why this wouldn't happen:
1) Evil customers could just resell an eventual "bonus Steam key" and that means losses for CDPR;
2) Steam won't allow "reverse GOG connect" it because they don't profit from it, and they are in a market position that allows them to act like this. because they know that if people want a game on Steam, they will simply get it there.
It is a matter of whether you want to support CDPR more (and have CP2077 truly DRM-free in the process) or have the game in your favourite library.
Steam already has a way of generating additional product keys and as far as I can tell they don't impose any significant restrictions for generation when dealing with big titles and publishers. Moreover, there is a way to grant a product license directly to user's account, which eliminates the possibility to resell that license. In my opinion, that is more a question of CDPR taking time to discuss this with Valve and I was hoping to get some sort of official response whether they are going to attempt this or not.