Sounds definitely like something I would be really interested in. If there was a way that anyone with moderate funds could build a device or method to do the Street View job while hiking, and it was propagated enough to have a community like the global GeoCaching community, that could be one vector to try out.
Maybe post on Reddit's http://www.reddit.com/r/SomebodyMakeThis as well?
What I don't have is any knowledge of is the costs of the imaging hardware you'd need - it would have to be fairly ruggedized to deal with the trail dust or if the backpacker fell. I don't know if consumer-grade video cameras that mountain bikers use would be good enough.
I'd start with the most heavily hiked trails first, South Kaibab and Bright Angel in the Grand Canyon, Half Dome in Yosemite, South Rim in Big Bend, and so on.
Luckily myself and a lot of my friends are trail runners, so I could probably get a few of them to do video trips in exchange for airfare :)
It does look like google has started to do this: