Yesterday CD Projekt RED released the first trailer for their upcoming cyberpunk game, Cyberpunk 2077, which you can view here. Hidden within that trailer was a message revealing the impending announcement of what we can only assume is The Witcher 3:
"And that's not all that's new. We are about the reveal our other project which is much closer to being completed and yes, it will also be a fully open-world game with an intense story. You can probably guess the game we're talking about :-) On the 5th of February it will all be clear."
Given that the only IP CD Projekt RED have worked on besides the upcoming Cyberpunk 2077 is The Witcher series, it's being widely assumed that this is a reference to The Witcher 3.
The message also indicates that The Witcher 3 will actually release before Cyberpunk 2077, so those interested in CD Projekt RED's new IP could be in for a very long wait.