Yeah, this is something that's puzzled me for a while now. It appears federation and instances only splinter like-minded communities. !headphones@whereveryourlemmy.instance is just one of too many examples.
Scattered is ok. More choice. Less moderation elitism.
Anyway headphone communities were always scattered. Headwise, Head-Fi, SBAF, reddit, Discord.
Survival of the stronger I guess. 🗡️
It is interesting. I think the solution would be that the mods of each need to cross-advertise until a better solution is available, or simply decide which one will be the one to rule them all and have the mods in the others direct everyone to the chosen one.
An issue will arise if the communities don't want to cooperate with each other. In that case, they just need to be treated as separate communities that may have overlapping members.