Evan Dodds has some good news today - it seems this did get included in RTM!
Things to know before you start using memberOf attribute in filters
Before you set out to use it in your OPATH filters, consider the following:
It's generally not advisable to use the memberOf attribute to filter stuff, because it's a back-linked attribute. (Nevertheless, in many situations, the use of this attribute to filter recipients is inevitable). Using back-linked attributes is not very efficient from an AD perspective, and thus best avoided if possible. So what are back-linked attributes? If you answered "an attribute that's not a forward-linked attribute" you wouldn't be too off the mark :)
Jokes aside, back-linked attributes like memberOf only get generated when they are accessed. In other words, they are not stored in the AD object you're accessing. For instance, the memberOf attribute of a user/contact/group is generated from the member attribute of groups. Does the low-performance part make more sense now?
Unlike LDAP filters, the actual attribute name - memberOf is not used in OPATH filters. The filterable property name for OPATH filters is MemberOfGroup.
Like LDAP filters, you need to specify the distinguishedName of the group you want to use. For example:
"MemberOfGroup -eq 'CN=Sales,OU=Distribution Groups,DC=e12labs, DC=com'"Evan just blogged about this - read more about it on his blog, including his example that shows you how to get the distinguishedName of a group in a variable, and uses the variable in the recipient filter.
This is great news, and a big help for folks who need to use group memberships in a recipient filter.