In my experience, your chance of success will be higher if it isn't called a "geocaching" merit badge. The implied scope needs to be greater than simply going out and finding caches. They should be competent in all aspects of GPS usage, understand the basics of how the satellite system is used for navigation.. know how GPS units are used in various industries i.e. forestry, transportation, engineering, mapping, land management, etc. Also, having a true understanding of longitude and latitude, and be able to function in degrees and minutes or in UTM. Application of the skill to everyday life will grab more interest in BSA than simply presenting it as a tool for finding caches. The process can take years. It may be the next generation that is offered the merit badge, but in the meantime take your kids out caching.
PS.. the push must be in Dallas. Your local guys may nod and agree, but the decisions are made down there.
BSA has already added GPS to the camping MB ....I also think it would be a cool MB to do but scouts need to learn their way through the woods with a compass as you don't get a good signal in the woods to a gps.