Something similar to the 5D MKII with better AF would be more than enough for most just a slight upgrade would make the camera much more useful!
The 1DX 18mp sensor (keeps the MP lower than the 5D MKIII, 7D body and sealing, 7D 19af autofocus system so not to compete with the 5D MKIII and 4.5fps to be useful but not compete with the 5D MKIII think that would be a great start point.
Possibly a touch screen? Similar to the 650D that you can turn on and off to suit both types of people. Must be high res too. Similar video to 5D MKIII.
The 1DX sensor and 51k native ISO (without extensions) plus "7D body and sealing, 7D 19af autofocus system". How about that at 2k USD?