The venerable "cool URIs don't change" https://www.w3.org/Provider/Style/URI (by Sir Tim Berners-Lee himself) has good counsel what NOT to put into an URI. Among those:
> Software mechanisms. ... give-away "look what software we are using" bits in URIs.
There is an extra paragraph stressing this also holds for domain names.
Now "Mastodon" is a particular technology. So all customary "mastodon.*"-type hostnames are ignorant of TBL's good advise.