So, is this a feature you’d like to see built on Mutable? I’ll consider it, but it might take some time for me to get to it.

yes please! Of course, no rush though. I do think it should be a standard, however.

True.. is very much group signaling but I guess depends on the amount of legit users on the NIP-05

If someone's allying with a domain that spams my periphery with noise, i really don't care about them and wouldn't bother validating their signal as a user in the first place. Being able to have a nostr address point to so many free domains, and they choose the spammy one? No thanks, i'd rather block the domain by default. If they want to be seen by me, they're welcome to do the "work" and change out their address.

Its a bidirectional relationship as well. Maybe I only want to communicate/see users from @mynostrcommunity.com or want to block anyone that does/nt have a NIP-05. Its about enabling optionality and multiple types of barriers. What ultimately makes nostr robust as a whole ecosystem is that there's no single criteria to game. You'll break nostr eventually if there's a singular best & unchangingWoT metric that all relays and clients use. Good luck doing that when every user, relay and client have even 10's of WoT algorithms to choose from.