The time estimation assumes that the implementation will be done in Xvnc (or perhaps Xvnc/vncconfig). It could fork off a process that executes scripts in a xconnect.d/xdisconnect.d directory. To me, this looks fairly easy to implement.
Hmmm... There is a notification system already in place for connect events (VncExtQueryConnectNotifyEvent).
Note that sessionreconnect.d already exists, but that is run as root on the master. The issue here is about running things in the session as the user.
*** Bug 2466 has been marked as a duplicate of this bug. ***
There is no clearly specified use case here, and it merely *might* be part of the solution for things like bug 493 or bug 7605. Closing this bug in favour of focusing the discussion on the specific use cases we want to solve (i.e. the other open bugs).