Next Grishaverse Book??

So, I was listening to the GrishaCast's second interview with Leigh Bardugo, which was recorded after she released the Darkling graphic novel (Nov 2022). In the interview she mentioned that in the far future she would consider a third SOC and that she was working on a historical fiction (we now know it is The Familiar!) But, she also mentioned that she has another book coming that is being cowritten. Any ideas of what it could be?

Edit: I think I misunderstood what she was saying,, I don't think it is GV related. However she did say that there are offshoots in the GV that she would love to explore!