this is only a ipb vantage. I personally own 4 dedicated server, and i want to host the chat on my server (the pages here at ipb are really slow to load, sometime we found a load average of 9 on the board! plus i'm in italy and the ping is bad...)
Maybe they are already listed...
in order of importance:
1) post history (when an user edit a post)
2) the ability to soft-delete a post
3) Notification system (as vb 3.8)