Several times.Besides, wasn't this question asked last year?
I think it's a good idea, and has been suggested a few times on these forums. I wouldn't rule it out, but would have to be some very tiny GPS chip and plenty of battery in the band. Probably better to just add GPS to the watch as standard functionality and have straps that just further the battery life and would likely be recommended for prolonged GPS usage.
Even better would be some kinetic re-charge system, but I'm not holding my breath just yet.