It's pretty clear from discussion on dev forums that Apple would simply never allow any such third party app - it would require an abandonment of sandboxing iOS.
Regular old chicken of the VNC can be run on a j'broken iDevice - but iOS will never support such a thing. Just in principle alone, it goes against the core security model of iOS.
Things like eggplant also let developers get remote shared access to their apps for testing, interface refinement and so forth. But the are restricted to sharing just the specific eggplant-enabled apps. But other than those sort of app-specific sharing tools, there is never going to be any sort of whole device remote, or OS level access possible in iOS.