Currently there is no way possible to grant a group of users Kick/Ban/Register permissions to specific sub channels. If one wanted to create a moderator of his own specific sub channel and not be able to influence others outside his channels, the functionality to do so doesn't exist.
There are 2 ways I propose to fix the issue.
1) Allow acl's to grant Kick/Ban/Register Permissions in sub channels so admins can lock down moderators to their own section.
2) Allow the option "Applies to sub-channels" to take on specifics defined in a field, whether that be a variable like the "channel name" or a range of "channel positions" for a group. You could also allow channels to be added as an acl "group" through the Groups tab, then put the group acl in the field to specify sub channels.
With either solution, more power can be granted and controlled in mumble servers. I was looking at this as a means to create different divisions in my guild's community. Each Channel is for a different MMO or game we are involved in with different moderators per game. I could grant them all the permissions applied to the whole server, but the possibility of them interfering with other division's activities is a threat to security.
Please consider this functionality and offer your supporters more usability and power. Thank you.