It would be neat if accessories like this were bands. Considering how small GPS chips are nowadays you could fit that and a BT module with small battery inside a band. The Apple Watch has a diagnostics port (with a cover plate on shipping models) that some speculate could be used to power such accessories in the future. Even if it can't, you could still put a micro USB port where the band connects to the watch to hide it while in use, and when you pull the band off you could charge it with that port.
Anyone want to make a Kickstarter? I have a background in design, photography, web development and marketing. We would need someone who can specialize in packaging a bluetooth chip, gps chip, battery and any controller chips to tie it all together in a thin band. We would also need someone who has manufacturing knowledge or contacts, and someone who has experience with materials design who can take design concepts and make them into a functional, ergonomic, aesthetically pleasing and premium feeling final product. The projected sales numbers so far skew heavily towards the sport model, so I would guess there is a sizable portion of the market who would be using this for fitness tracking. However, there would have to be a clear benefit of GPS over a motion co-processor and barometer combination. More accurate? It would also help you track distances on a bike. It's my guess that bike riders typically are more interested in viewing the path they took vs. runners. If there isn't a clear benefit to runners that could limit the market substantially.
