for mobile, I believe after either umbrella comes out or when the last two new fighters come out in 2022, the latter makes the most sense to me since the new story will be able to add in these 4 new characters as a challenge in story mode for the first time and that will add a lot more variety to the new story gameplay-wise
Two story options: 1. Current: More story for the present day, Skullgirl Marie crisis. Story modes for Annie, Umbrella, and (as StarUrania mentions) the other two (probably Marie and Black Dahlia). Could have "what-if" non-canon endings (e.g. "destroy" the Skull Heart or make a wish). I'm hoping for one unified, definitive, storyline. Like, what happens to everyone, who defeats Marie, and how tall of a building does Beowulf suplex Vitale Medici off of? You know, the usual questions. 2. Future: A Skullgirl appears every 7 years. So a true sequel, the REAL Skullgirls 2, should happen seven years in the future in their timeline. So if you want true continuation, look there! Would be weird though. Can you imagine a 20 year old Peacock?
Didn't originally the plan for the second part include Eliza as the main villain? And the third part would be about fighting Aeon and Venus? It might hint about some major changes in the game universe.
Of course, the plan might be different now, but who knows.
Which makes me think about Eliza's origin story, that we definitely need. It might be even a literal origin of Eliza, the club singer persona of the millennia-old bloodthirsty demon.
Oh, how we need some new story modes.