The Phantom is lacking a few things I need. First of all, it is not waterproof. I will often be shooting over water. I have rigged up a float system that might save it from sinking but the electronics would likely be damaged if it lands in the river.
The second issue is weight/flight time. With the camera in its waterproof housing, FPV transmitter, OSD components, locator, floats and possibly a gimbal, the weight is pushing the limits of what the Phantom can lift and shortening the flight time. Adding a second battery would increase the weight, require more floatation and make it fly like a pig. I am also considering shooting stereoscopic video which requires lifting two Gopro cameras and housings.
For these reasons, I am considering building a waterproof hex with carbon fiber shell and heatsinks for the electronics. It would require a breathable window for the altimeter.
It would save a lot of money if I can reuse parts from the Phantom.