That is literally the way it works now. As an example - go to https://phtn.app/. Photon is a UI for lemmy. That specific website is hosted by the developer and you can log into any instance. I think Alexandrite and Voyager webapps act the same, but I haven’t tried them, so can’t be sure atm.
I did not know that! Thank you!
What do you mean by implementations? Is this closer debian vs rhel or more like linux vs bsd?