I don't see how we've lost any time to the "SPF circus". SPF
and RMX haven't affected RFC 3597 deployment; it's been the
other way around. SPF is being adopted and deployed precisely
because it can be (right now) in TXT records, while RMX was
hindered due to its RR type requirement.
The brutal fact that must be faced here is that designing a
spec is easy, getting a spec deployed is the hard part.
It is very easy to get a spec through a standards process
without building any of the support that is required for
deployment.
This whole argument has centered on persuading network ops
to deploy MARID records. That is as it should be because at
the end of the day the spam filtering companies are not going
to pike at XML, it is an insignificant overhead given what
they already do.
Microsoft has ways of persuading network ops that are not
generally available. They also have rather a lot of experience
in incremental transitions of large crufty 1980s technology to
a modern architecture.