Given that a wildcard record:
*.example.com IN TXT "Some text"
will match
_ep.subdomain.example.com
just as easily as it matches
subdomain.example.com
Right, absolutely. Wildcards ARE a non issue except in one respect.
An administrator can create a TXT record that matches _ep without
difficulty. The only problem is that it will match everything else.
Selectivity is lost.
In other words when we are dealing with wildcards the result will be the
same in that particular case as if we overloaded the unprefixed TXT record.
In all other cases we get the selectivity we need.
People who are unable to enter _ep or _marid as a domain label can even use
wildcards as a way to introduce the label.
The only thing we need to make sure of then is that we do not rely on _marid
as a failproof means of getting a MARID record.