Written briefly cos it's late at night, but rather than arguing either/or,
this is a suggestion along the lines of "pay for it only if you want it".
Suggested idea for SPF extension for a sample domain schmerg.com with a
standard SPF1 record
v=spf1 mx -all
SPF v2 (or 1.1 or whatever) keeps the existing syntax and use of TXT records
in DNS, but also allows the specification of a URL that holds the XML record,
hence making XML available to those who really want it, but keeping
arbitrarily large XML out of DNS records
v=spf2 xml=http://www.schmerg.com/spf.xml
or
v=spf2 xml=http://www.schmerg.com/spf.xml mx -all
... meaning "if you don't want to pay the price of setting up a full TCP
socket, talking HTTP (or whatever URL is specified), and parsing XML,
consider my record to be empty (first case) or 'mx -all' (second case), but
if you're willing to pay for more detail please retrieve the specified more
detailed XML record (which, if retrieved and considered, replaces rather than
supplements therest of the SPF record in the DNS TXT record)".
Then let each domain decide if they want to publish XML (by specifying the xml
URL or not), and let each MTA that wants to check XML decide how much effort
it's willing to expend in doing so.
This way you get the best of both worlds - let the 'market(s)' decide how much
they want XML...
Cheers
--
Tim