Well, technically it's possible, though I don't know if anycontrol-panel publisher allows it.
Here are the necessary steps, just in case John is reading and wants to implement it...
1) set up the reseller with unlimited space, mailboxes, etc.
2) restrict the reseller to only being able to sell packages set up for her/him.
Billing isn't really that hard either; if we were going to do this (we're most likely not), we'd want to get emails whenever a domain is created (DA may very well do this now) and then afterwards use a script to monitor the domain's continued existence on the box.
Jeff