Okay, your responses, including from some I consider Sensible Information Technology Professionals, indicate that an in-character-only Mastodon instance might not be as impractical idea as I'd originally feared.
I could very much get into this. Let's keep talking about what this would require.
@zebratron2084 I'm willing to help with support text, brainstorming, worldbuilding, etc, but I'm afraid I'm not able to be any help with techy stuff. XD but I want to be helpful! *vibrates*