I’m suggesting a whitelist, that each peer has to put in a substitute list of vlemmy.ml==vlemmy.ml to re-federate.

I don't see any inherent problem with that suggestion, though it does create something of a sticky situation with things like canonical links. It also kind of goes against what I've so far perceived as a "low-maintenance" operations ethos from the project maintainers, so I'm not totally sure if they'd greenlight it. Technically quite doable, though.