Addon Modules and cPanel
It would be great to have addon modules work with cPanel, for eg.
A client purchases 10GB addon for his current plan and it is automatically added to his account on cPanel.
If changes are made to an account on cPanel like adding more bandwidth or data, cPanel will want to change the name of that users package. I have also noticed if you keep the client on that same package but just add the space or bandwidth after a restart for example it will reset to its default package thus forcing you to put them on a new package name.
It would be great if WHMCS could work with cPanel to have these sort of features going.