Some of my clients started asking for a control panel where they can check their bandwidth, reboot, reload, etc.
So i'v started it, and at this moment it already do:
OS Reloads (vzctl destroy & vzctl create) (not completly ready yet)
Reboots (vzctl restart) (max 1 minute)
Bandwidth stats (gets traffic from iptables every 15 minutes)
Hostname change (max 1 minute)
i suggest you have a look at hypervm.com for some inspiration. It is a commercial product (where yours would be GPL'd maybe ??) but it has a pretty full feature set already, and the forums there have a decent list of feature requests for the next major release...
If your going to build something new you may as well check out what the competition is doing