All of the above, a nostr TLD sort of implies nostr is one sort of thing, but it's capable of powering lots of different types of apps. It would be like having a ".net" tld (which of course we have, but it's still silly).

ICANN is one thing, but specific tlds are even more centralized, c.f. xyz. If most nostr things ended up using the nostr tld, it would be even easier to wipe them all off the face of the web in one shot.