Basically, web hosting panels of today automate a lot of the process, but there are still many things which are poorly done or not even handled.
For example, in WHM for the usage of clients, you only get a number. Just imagine how much more useful it would be to 'see' their usage, as a box which is the exact size of what they use. It could even be coloured based on their status. You could see at a glance how much space is being eaten up by overdue clients, suspended clients, active clients, your top clients, etc...
Another thing that I feel is not handled well is support for multiple websites. Many clients like to run more than one website, yet there's not really an effective system to help them manage them all. You can get a reseller, but that's really made to manage lots of accounts (run a web host), and has all kinds of functionality you really don't need. In the WHM, a website is an 'account', and aren't really grouped together by the client except in resellers.
Another thing that's really lacking on web based panels is speed. Specially when you start dealing with lots of accounts. It's inefficient to wait for the WHM to load a huge list of accounts, in a fancy AJAX interface, when you already know the account you need to modify.
Finally, I see a ton of threads here about 'backup systems'. So it really seems that there is a desire for a backup system which is well integrated into the full system, and automated, and client-controlled. Imagine if your clients could restore their own backups after a disaster - how much easier that is for them when compared with you restoring them in sequential order. Backups are a huge inefficiency with web hosting.
What about referrals? Being able to see a visual tree of where your customers came from? Wouldn't that be interesting and somewhat useful?
But obviously, this is only hitting the surface. My goal is to improve the overall quality of hosting by making it easier to provide a better service for your clients.
So really any ideas to do with control panels - what you really like or wish existed. It will take me a while to build it all, but still don't be afraid to ask.