CoP does not currently do anything fancy on register/unregister/drop but it (like most everything else)
should do sensible things when a user is added/removed.
I don't think anyone disputes the need to be able to do
package/site specific things in such sequences, the only
question in my mind is whether we want to do all this via
service contracts (our only real callback mechanism right now)
or with something lighter weight (or maybe fix service-contracts to make doing the lightweight version easier
than it is now).
At a minimum I would like a version of the tcl binding
acs_sc::impl::new_from_spec which did not store anything in the db and hence could be easily changed/upgraded.