The mems most likely to graduate from hololive are the ones who are less interested in singing and dancing. You may notice that these mems are not consistent. For example, Kronii started out hating the idol side of hololive, but has become more agreeable to it over time. Fauna never did.
My prediction: Botan and/or Kaela are next. They're just the giggly gamer girls; they don't want to shake their asses on stage, but hololive is heavily pushing them in that direction.