SHOULDs in this section make me (as resolver implementor) nervous. It
would be much simpler for resolvers if these were MUST because resolvers
would not need to worry about missing A/AAAAs in ANAME queries.
SHOULD means you should do it unless you have a real good reason not to do so.
Records in additional section may already be omitted because of truncation, minimal responses, ...
With resolver implementer hat on I would like to see either:
a) Removal of additional processing because its current form is unreliable.
b) Some behavior which is guaranteed to give all address types + signal,
that it is supported (so we can distinguish no addresses from missing
ANAME support). That might be useful as shortcut for "all address records".