Playing as Ciri makes no narrative sense to me except that it's a popular and familiar character.
Ciri is the central catalyst in the Witcher 3, and at the end of the Witcher 3 she stops finally running from her destiny and saved the universe, all while doing it by gaining what she wanted the most, independence. The Witcher 3 more or less concludes her story.
Ontop of that, she gets everything else, a stable family (If you choose either Yen or Triss) and her lifelong personal goal of becoming a Witcher.
It's not that Ciri can't do interesting things as a witcher, but the big question is what does Ciri want that she doesn't already have?
Ciri won't work just by her desire to be a witcher alone, she already achieved it. Dealing with her newfound independence? Seems low stakes. The only thing I can think of are cliches like killing Geralt and/or Yen, and go on a revenge arc, or we go back to ruining the Witcher 3, or retconning Witcher 3, with big end of the world scenarios. That or they make up non-organic reasons for her.
Yes, the time skip will help, giving her new motivations, new interests, new characters and new problems. But at that point, that's not the Ciri we all recognize, if we're going out of our way to create an entirely new identity for Ciri that nobody recognises, then why didn't we start with a new Witcher?
Tldr: Why make Ciri the main character? After the Witcher 3, it's hard to organically make a character arc with the Witcher 3 Ciri, she got most of what she wanted and completed her character arc. If they reinvent Ciri with the multi year gap, then why not make a new character?