Note, however, that the two things can work together: communities can be attached to specialized relays (the use of which would be automatic, without users having to do anything) and specialized relays could mirror posts that use certain hashtags from other relays.

However, I think the most crucial kind of relay to have is the general, content-neutral, free speech, free of charge and privacy-preserving one. Nostr makes it possible because running a relay is much cheaper than running a classical centralized platform and it can be a good way of contributing to the core human right to freedom of speech. It'd be nice to see Nostr relays from relevant non-profit organizations.