I'm sorry, but no. The point of the fediverse is not to spin up niche communities, since we already have forums. You want to be part of a niche small forum, go spin up your own bb instance and run a niche small forum.
The point of the fediverse is to recreate the global social networks that are twitter / Reddit / etc, but to do so using open source servers that are decentralized and anyone can host.
Again, federation is not a user facing feature, it's an architecture / implementation detail. Fediverse enthusiasts are like train enthusiasts who love every detail of how they're built and their history and how much philosophically better they are than cars, but none of that matters and train networks will fail if they don't provide quick and convenient transportation to their users.