Being able to tag chats with keywords would be nice. Being able to pull chats into docs easily would be nice. Being able to pull chats into more than one doc -- not just move, but tag/reference/copy. Global tags (with ACLs) as well as team and personal tags (also with ACLs) would be fantastic. Don't forget read and access ACLs, not just write ACLs.
Email integration would be nice. Emails -> IM, so I can read IMs and emails in one app. IM -> email (right-click on a range of messages, click send, get placed in $MUA and edit).
Don't forget retention controls, support for on-prem, etc.