I think it is a great idea. I find that so many just post their State or just USA and that is not helpful at all. Even a few are posting fictional locations. The information you are proposing is not a big invasion of anyone's privacy. Bolter's going on cross country excursions, such as Builders IRWIPI adventures, could use it for social purposes or emergency assistance if they break down on the road. As proposed it would be only those who want to participate so those who have anti social tendencies could opt out. I say go for it.
