The main issue I notes about this is that, if I wanted to set up I Lemmy system, I would go for Lemmy itself, not another tool that I then had to configure to work as Lemmy. Same goes for a microblogging service, I would set up a Mastodon service, not a service that needs to be configured into being Mastodon.
As for it being used to develop mockups for new Fediverse experiences, I don’t think it will do that either, since if you are doing a mock-up, you are looking an not only how a possible new design would work, but also the backend, to get a sense of what is needed in terms of storage, compute and other software layers.
A system this diverse will be very dificult to reduce the complexity and give a good idea of what kind of environment is needed for someone to invest.
What it could do is serve as an inspiration tool for students, it could absolutely serve as a technical demonstrator of the ActivityPub as the teacher can build simple systems and show what parts of activity pub they use.
I remain skeptical of the future of this type of system outside of the classroom environment, though I do wish the developers all the best