Dave, I understand you. This may seem like a solution in search of a problem. The reason I see it differently is because of the recent increase in the number of and participation in trail running events in my region and in the U.S. I will poke around in some trail running venues and ask some trail ultra runner friends what they think about some kind of measuring standard for single-track races. In the Mid-Atlantic area, this kind of event is flourishing. There is constant discussion among participants and organizers of these events about how long/short a particular course may be compared to its advertised distance. These differences are usually non-trivial. An 8+% underestimate in a 50-miler means participants run at least 4 miles more than they expect to. I ran a trail "marathon" once that GPS-wearing runners claimed was more like 29 miles. I believed them, based on my intuition.
Since participation in trail races is large and growing, why not establish some kind of criteria for distance estimates so that trail race runners enjoy benefits that are at least "somewhat comparable" to those that runners of certified road courses, or at least as reliable as Mike Sanford's "Gravel" or "Off Road" criteria? These GPS measurements would adhere to procedures and quality checks that we devise and test. For instance, establishing minimum GPS device track log "time slice" and memory requirements. Requiring measurements be taken only when there is no overhead canopy would be another standard.
I agree with Mark that "a carefully done GPS measurement" would be more worthy of our trust than any other currently available method for single-track events. Hence, an opportunity to establish sensible guidelines or measuring requirements for some kind of USATF imprimatur. Something better than "Random Joe with his Forerunner", which is all these athletes have available to them today.
Establishing a single-track measuring system can provide distance and performance comparability between trail events. It will allow for "truth in advertising" for trail race distances. It will help line up trail runner expectations more closely with whatever the actual distance run might be. I believe it is a service to the running community that we can and should look into.