Well, given that Witcher 3 is out and they've basically declared that they're done with the Witcher franchise
They never claimed that The Witcher franchise is over that I've seen. They did state that the story of Geralt of Rivia has come to an end in the franchise, but they suggested that there were other possibilities to explore in the franchise if they chose to do so in the future. Someone speculated that Ciri would make an interesting protagonist in a future Witcher game although I don't recall if that was someone at CDPR, or the person interviewing them or someone else. With the popularity of the franchise as a whole, in particular of The Witcher 3, I would be surprised if CDPR throws in the towel on the entire franchise however. They're focusing on Cyberpunk 2077 at the moment of course, and the spinoff Gwent game (unless they've subcontracted that out like The Witcher Adventure Game) but they certainly could be dreaming up possible future Witcher titles. There's a lot of different things they could do to expand the franchise in different ways.
- A prequel story of a younger Geralt being taught by Vesimir and becoming a witcher.
- A reboot/remake of The Witcher 1 with modern graphics/engine/controls.
- Spinoff stories at any part of the timeline with one or more of the other well known Witchers as the protagonist (Eskel, Lambert, Vesimir ...)
- A new game based on Ciri placed in time after The Witcher 3, possibly called something else because she's not a witcher herself and I don't think she can become one if I understand the lore. Let's call the speculative game "The Ciri Chronicles". The game is an amazing open world VR game. :)
- They could license the IP to Telltale to do one of their point and click style games.
I'm sure others can come up with a dozen other interesting ideas where they could go in future titles if they wanted to. I know some people would end up being pedantic and want the series to end where it is now and moan about it likely because that's the Internet for ya, but I for one would sign up for any future title of anything along the lines of what I suggested above, or pretty much anything CDPR might come up with. I'd have no reason to doubt them after what they did with Wild Hunt. :)
But... first things first... Cyberpunk 2077... :)