The apostrophe is gonna get dropped eventually. Same as it did for 'net meaning internet.
I doubt fedi~ will be remembered after awhile. It'll be seen as pedantic, technical, or old school.
I don't know if people are generally sci-fi enough to think of you as on "planet Lemmy" but it would have a bit of snark like saying you're on planet Mars. Could be a good subculture lingo.