Even a trivial implementation without support for partial updates (ie: if the seq number of the client differs from the server, then a full update is performed) would still be quite valuable.
The "big win" here is for this to be implemented for the roster.
This is probably a 4.0 task and placing against that release in hopes of getting a dev to code it up.
Included in RFC6121
Whilst recommended, Roster Versioning does not appear to be mandatory for compliance with RFC 6121.
This code change just went into master and will be in Openfire 4.2 beta, testers would be greatly appreciated. Can continue this issue if problems are found.