I'm not sure how to respond to this question because CP2077 isn't out yet and the CP concept may very well go beyond one game. I say this because looking at it from the perspective of after CP2077 is a hard question to answer. More CP is presumably a very real possibility. In other words, sequels using the CP setting. So it feels more appropriate to answer the question in the context of after the CP concept has been exhausted.
If the point is reached where the CP setting is exhausted, whether it be temporary or permanent, I'd lean toward a continuation of the Witcher or a new idea altogether.
It's probably safe to say, going off existing information, Geralt is over and done with. I could see continuing that setting with another character like Ciri but it probably wouldn't be the same. In spite of this I think this world setting still has quite a bit to offer. So I could very much see an extension of The Witcher. If this is the route taken I'd prefer they hit the restart button and use the same world setting but at a completely different moment in time. Well before or after the time period of the original three games.
If it's a completely new concept altogether I couldn't say. The options are limitless. There the only thing I can think up is to tell CDPR to surprise me.