Maybe one day there will be an SPF record type. Then the DNS servers
could optionally compile the SPF record to a simpler (less expensive)
form, automatically! Even "include:"s could be pulled in, as long as
the TTL is obeyed, and the SPF record re-compiled when something
expires.
That would be awsome. But even then we'll have to support 'legacy' SPF
clients, and they will seem awfully expensive by comparison to the
server-compiled SPF records, but we'll be stuck with them.
And how is this any better than the existing 'problem'? You are
proposing removing some processing and traffic in favor of more
processing and bandwith. Your proposal involves changing DNS servers so
that they would have to take a 'source' (i.e. SPF Classic) TXT record
(which they will have to keep on hand for periodic recompiling) and
compile it into a all-IP SPF record. Your proposal now also requires
that the authoritative DNS server for this domain must either keep in
cache every piece of information to compile the record or periodically
go out and re-request this information. So all of the bandwith and
processing that you propose to save has been reconsumed.
Marc