The Witcher universe is perfect for more storytelling, but it is time to leave Geralt in retirement and establish a new protagonist. I think the way to return to the Witcher universe is a series of 2-3 smaller Witcher 2 size stories to introduce new characters and political situations. These would be the "short stories" setting the scene before a larger game (the full novel). The smaller games could even have different protagonists, who all appear as major characters in the later big game. Short stories style games would also let them experiment with different types of protagonists and gameplay. For example, they could have a game played as a mage instead of a witcher, or even someone exotic like a higher vampire. Then for the big game the new witcher is the primary character, but at different points we might play as the other protagonists from the short stories.
Witcher 4, Episode 1: New witcher character is introduced, along with a new location (one of the countries along the Yaruga River for example). This episode introduces the protagonists for episodes 2 and 3.
Witcher 4: Episode 2: Protagonist is a major character from Episode 1 but with different skills/mechanics (a mage for example)
Witcher 4: Episode 3: 3rd protagonist in a new location, with intrigues related to episodes 2 and 3. This protagonist might be non-human like a higher vampire similar to Regis from the books.
Witcher 5: Big Witcher 3 sized story. Episode 1 witcher is the primary protagonist, but at different points we play as the episode 2 and 3 protagonists to fill in other parts of the story.