I suppose it is good to rotate IP, so players will not get fed up with another witcher. However it need to care for IP, releasing new edition with each generation. So more Witchers for us, but mix it with something.
As for popular genres:
Urban Fantasy, with all vampires hype you could find niche for some modern detective story with super natural themes, kina like Supernatural, or American Gods. TellTale Fable (Wolf among us) was somehow original. It could be World of Darkness universe, however it is owned by Paradox ent so they may have own plans.
Superhero serious. Superhero games are weird unpopular in quantity. We have some spiderman or Batman, and Infamous. But it is so little.
Oriental cRPG is actually good, since we have suprisingly few games in it. Jade Empire was o long time ago.
Game of Thrones is great universe, however i am somehow suprised nobody took it already. Maybe there are reasons for that.
Actually there was computer game with Game of Thrones, telltale one. And it is not even big project so license maybe is not that expansive.
This may be better idea than one may thought.
It is hard, since it depends what is avaiable. Some ideas:
Lovecraft Horrors, possibly in Dieselpunk or Steampunk.
Hard SF in Spaaace.
Para Historical Europe with a bit of magic (like 30 years war) with strong folklore.
Warhammer 40k could be fun. It has decent line of strategy and action, but no crpg. When some space inqusition would be hot
Or maybe it is empty question. CP has great potencial for sequels and for being IP. And CDPR is not that big to make 2 big games at some time. And we still want some Witcher in future.
There is also option of taking existing IP (witcher) and making completly different game of it. Playing as noblelord on the quest to become the king? Or rpg but this time as Mage. Or diablolike with some witcher (isometric, more Torchlike) more combat oriented than heavy story. There are different tastes for games.