As a game set in the Witcher universe - why not?

An MMO game similar to the Witcher games - no. The games are about choices and consequence, and it would not work in a MMO. One of the characteristics of MMO's is that the world must be static and persistent.

No way I'd play a The Witcher MMO. It simply doesn't fit, i think.

I'd rather play a Mass Effect MMO over a The Witcher MMO.

Depends, maybe if it were free to play, but probably not. I had my MMO experience with Ultima Online, I'm pretty much done.

Maybe, i it was possible to play something like a giant kikimore able to go squishy-squashy hither and yon.

No! I'd want Kotor 3, erm, I mean Witcher 3...

No, I wouldn't play it. But they would be smart to make one.

You mean would I play WoW and think about playing a Witcher MMO? Until that abomination goes under and all the other companies salvage what they have done right with MMOs I don't think there's room in the market for another one. I'll admit it would be nice to explore the Witcher universe in more detail but I don't think an MMO is a good way to do that.

Only if I could collect digital cards of other players' avatars nekkid after engaging in cyber-sex (to be dubbed cyber-coitus or cyber-witching in game).