First; a device, like a pitching machine, that can be used to accurately measure the flight qualities of a disc repeatedly. This would aid manufacturers in quality control, and give the consumer more information before they purchase a disc. I know that this is not a new idea but it should be a priority.
Second; like it was said above, RFID tags. I wonder how close you would need to be to your disc before these would actually work though. We use these at work to manage our inventory and even with the giant handhelds we have you still need to be within about 20 feet, so I question whether a small device like a smart phone would have enough power. It could still be invaluable if your disc ends up in some very thick, dense brush or underwater.
Third; indoor courses. Where I'm from there are quite a few old and vacant factory buildings with several hundred-thousand sqft. of empy space. Would love to be able to still play or at least keep my technique fresh when there is 2 feet of snow on the ground. I'm sure it would be a money-losing nightmare unless you could draw enough people, but would anybody else utilize such a place if it existed?