Are you a developer, what kinds of apps do you have in mind? I agree it may be a good niche for someone to get into. One good app may be some kind of scheduling/organizational app. Something that would be able to pull all of your assignments from your accounts and help keep track of them for you. This is the hardest part for me. Something similar to JobSlinger Plus, but with the ability to get Prophet, Shopmetrics etc...
Of course the MSC would have to agree to cooperate. Anything that makes tasks for the shopper easier is going to have a benefit for the MSC. So you never know if they would consider getting something set up with them a pay-off later down the road. The app could keep track of the status of the jobs, receipt verification, your rating, payments etc, there are many possibilities....Now my mind is wandering, lol.
Forgive my grammar and spelling on the boards. I am off duty.