I would like to see an mmorpg title from CDprojekt and I believe that this thread is not specifically about an mmorpg in the Witcher universe. It can be something else entirely.
However, one of the problems in mmorpgs is what I find as first come first served titles. For instance, we have Dota and LoL. Both have dominated the field of moba as they were released in times where moba games were not many. Many companies tried to follow the footsteps of Dota and LoL, but eventually failed. That's because Dota and LoL have already dominated the moba industry. I don't know much about the Old Republic, but I also believe that no mmorpg introduced a similar world before the release of the Old Republic, which I think makes it one of the dominant titles in mmorpg.
In addition, transitioning between existing and new communities can be difficult. For instance, one can easily, and rightly, find that Dota or LoL's community is toxic, but still we usually choose to stick with such toxicity over trading it with another community that's probably going to be also toxic, or decide to leave them both entirely. Also we find in many instances that the time we invested in a certain mmorpg and its community can be quite difficult to trade them with a new title and new player base, especially that it's almost impossible to keep playing two mmorps at the same time.
So I guess Cdprojekt would need to introduce an interesting world such as Cyberpunk, which I think no other mmorpg made something like that, in order to convince people to transition from different communities.