At the moment, there's no way to delete a user once he/she is registered.

It would be nice if there were better ways to deal with deprecated/old/spam users, instead of just activating/locking them.

I.e.
Users who haven't posted anything

• Should be safe to delete these users

Users who have posted something

• Prompt to remove all posts by the user (on delete cascade)

However, some organisations may want to keep a log of everything (prevent deletion).
In that case, this can perhaps be an option that only an Administrator can set.