I was just thinking an awesome MobileSubstrate plugin would be one that integrates Cydia into Apple's App Store App. This way, when you search in the AppStore or go in the categories section, there would be a divider that separates Cydia apps from AppStore apps. Then, jailbroken apps would install the way they currently do -- inside the Apt manager, and AppStore apps install the way they currently do. If this isn't feasible, maybe a seperate app could be made to manage both worlds?