While the permission system is really detailed and awesome, one thing I am missing is that you can assign server groups special permissions in special channels. Similar to Channel Client Permissions, where you can assign each user custom rights for each channel, I would like to assign a server group (A) for example special rights to join only some channels (but not others), while another server group (B) is allowed to join other channels but not the channels of group A.
I'm happy that TeamSpeak 3 moved away from the static 3 server-wide group (SA, Registered, Anonymous) and 3 channel-wide group (CA, Operator, Voice) system, allowing more custom groups, but a bit more possibilities would be great.