IMHO, there should be an RFC explaining that use of a TLD as a
terminal domain name was never intended to work, and should not be
expected to be supported by the Internet architecture or software.
Sounds good to me, although there is the pesky detail that 2821
ambiguously and 5321 unambigously says that they do.
Since 4409 that says that an unqualified name is often treated
relative to the local domain, perhaps an update to both 5321 and 4409
would be in order, specifically saying that in view of longstanding
experience, allowing undotted names was an error.
I'd suggest it should return to the 2821 ABNF, and say that in both
SMTP and SUBMIT, multi-component domain names are absolute. In
SUBMIT, servers may either treat unqualified names as relative or
reject them. SMTP rejects them.
ICANN has gone off the deep end.
News flash! Sun to rise in east!