I would just make it Jedha rather than a new Sith world (we already have one with Exegol). I like the idea of them heading toward Jedha, expecting a wasteland, but then see people living, thriving, actually being happy, in the aftermath of the end of the world. Maybe they’re just pilgrims, not living there necessarily. But it ties into this film’s theme of healing wounds.
Also, they say they’re going to the Forbidden Valley on Pasana, so it would make since that a Forbidden Valley on Jedha might have some ties with the Sith. Also, if Ochi is a Jedi Hunter, it makes sense to go to a Jedi world to find something important.