It's not that rare. NIP-26 and NIP-46 are kinda doing the same thing by very different means. Kind 3 relay lists and NIP-65 lists are "similar". Kind 10000 for mute lists is also done as Kind 30000 with a `mute` label. NIP-04 and the new NIP-24 will both do Direct Messages.

As Nostr grows, we will see more and more alternative ways to do similar things.