I just hope it doesn't turn out like email where you cannot use your personal domain without ending in a blocklist.
IMO domains (without subdomains) that NIP-05 verify only 1 account should be considered trustworthy.
Discussion
Maybe some free TLD might be discarded, but `.com`s and `.org`s should be good.
We are implementing premium accounts that are subdomains partially for this reason. The other reason is that some clients display username@domain.tld and others display @domain.tld even though both were registered with a username and not (-). 1 subdomain per user may fix that.