One problem I see with Mastodon is that it’s very community based. Right now, I’m on Mathstodon because it seems like a somewhat appropriate fit. I’d flip to social-qubit, but my work is heavily condensed matter. When a CM instance emerges, I’ll join, but then this will be isolated from the QI community on social-qubit (QI still features in my work as well).
Also, without a CM instance on Mastodon, I feel a nomad. And I don’t have the technical skills/time/money to make an instance myself.