This sounds kind of delightful. Even though I've come across a few solo RPGs and solo larps, I don't think I know any solo actual plays?
And the idea of some kind of epistolary actual play where you leap through one game and another in a single interconnected story, that sounds fun if done well but over ambitious. Are you experienced in podcasting at all? Do you have good sound setup? Feel like bad sound setup could easily kill an idea like this. Sounds delightful but also overambitious.
The only thing that bothers me about your pitch is I feel like you're trying to justify why magic can happen in the scifi world? "a quarantined world in a Stars Without Number setting, magic is real and functions for unknown reasons so on that world I can play things like Monsterhearts or Urban Shadows,"
I suppose this might be just me but I feel like when you cross different things together, you don't really have to justify it. You just do it. I love Carmilla, the youtube series based on the novel. I love JP the library ghost AI. Until that point, there's no evidence to suggest that AIs exist in the world, let alone AIs made from library ghosts. There's no context internal or external to the fiction on which we can infer such an idea. But a few episodes into the show, after simple honest vampire horror and raunchy drama, boop! Robot! Carmilla kept doing stuff like that. Throwing in not vampire stuff into the vampire show. But it stayed a vampire show at its core. It just had all this other stuff revolving around it.
You don't have to explain magic's intrusion into a non-magical world. So long as magic's role in the story remains consistent and coherent and interesting, you don't have to explain anything. People will pick up what you're putting down, and the science fiction or whatever will still be there when you want to go back to it. Undisturbed by the magic.
Vampires in space doesn't have to be explained. Does that make sense? Am I making sense?