I'm glad that the series has an end, and I hope it'll stay that way. TW3 is a great success, yeah, but which is the stronger brand here - The Witcher, or CDPR? I think it's the latter. Not that I have any statistics, but my gut tells me that gamers tend to stick to companies even when they have different games. How many players are there that care solely for Fallout, but not Elder Scrolls? Dragon Age, but not Mass Effect? The Last of Us, but not Uncharted? There are probably some, but I feel that most gamers who have a company they like, will enjoy most games coming from that company. If CP77 will also be a great success, I'm not so sure CDPR will have to be anchored to The Witcher for future hits afterwards. They're making a name for themselves, and that goes beyond just one franchise.
I'll be really happy if The Witcher ends on a high note with 3. It rubs me the wrong way when a company constantly revisits a certain world, even if there are many stories to be told there.
That being said, if they do return anyway, I prefer TW:Something (probably won't be named TW4 since it's not a continuation) to be completely removed from Geralt and co. A different witcher, a different time, a different region. Maybe even a character creator? To me, CDPR are at their best when they're free to create their own characters, surprisingly, and I'd like to see them with something that is completely their own creation. So if it's, unfortunately, not a new IP, then at least steer away from the books now and the familiar.