Maintained is a broad concept. All existing contribs work as they were designed and released at the time for a specific SME Server version with a specific application version wrapped into the contrib.
All 'official' contribs can be found in bugzilla and new ones can be inserted at request. Reason for using bugzilla is that the code can be reviewed and bugs can be reported. The contrib source code and the RPM package should be submitted to the official contribs repo (we have to many 3rd party repo's now).
As for maintaining, the owner is mentioned in bugzilla as per the 'assigned to' field. This filed will not change unless the original owner agrees or is no longer active. Submitting suggestions, patches and bugs or new ideas to the contribs can also be done through bugzilla.
As for orphaned packages, there are a few, e.g all the work of Stephen Noble or Darrell May. They are no longer active within this community for one reason or another (but we are still thankful for their work).
e.g. Affa3 is maitained by Arneaud and Stephane, smeserver-freepbx and smeserver-ejabberd are maintained by Daniel. (where there is also a the Prosody and Openfire how-to's).
We don't have dozens of developers developing contribs, so knowing them and contacting them is pretty easy.
My suggestion would be to start with a jabber contrib. Either update the existing one or package one of the alternative ones, that would be a good practice. Then Quality control comes into play before it can be released through our official contrib repo.