quoting myself from the event thread:
Nina Kosaka and Natsumi Moe I also discount because it just doesn't make sense.
That leaves Beryl LeRou, mom0ki, Waabyuu, Woozie Wannai, and Ayane Hylo as the notable recent graduates that haven't appeared elsewhere, with the GGN twins in the mix I guess. Almost certainly there will be at least one person who isn't actually graduated elsewhere as Cover doesn't only look for vtubers and/or lets them hiatus instead of graduate. See the quoted post for more speculation. For example I would count Miori Celesta and Wolfychu both as possibilities even though they're still active.