Milter-greylist

Currently milter-greylist is able to perform checks of SPF and will whitelist
messages that would be greylisted if SPF passes.

However, I'm in a slightly unusual configuration where I only greylist mail
which might be troublesome, and default to whitelisting.

For me, it would be really nice to be able to do the opposite, greylist mail
that fails the SPF check.

I was thinking about this as an option when it struck me this would be
significantly more flexible if it was a part of the ACL system.

Something like this:

acl (whitelist|greylist) spf (fail|softfail|neutral|pass)

Which would allow a great deal of flexibility in handling of SPF.

Does anyone else think this would be a good/useful feature?