I don't think there will ever be a grand tour in America, But I'm sure this will expand in the next few years. California is a hot-bed of cycling, and there is proably no where else in the US you would get so many spectators out. If UCI wants to increase their global exposure, then California is the place to do it. A tour of the whole west coast would be super cool, but I don't think the big pro teams would be down for anymore than an 8 day race. That being said, I'd love to see it cover a bit more of California.
I'd love to see it make it all the way down to San Diego next time, and I'm sure there are plenty of places in the Serra-Nevada foothills that would be great for a race, as long as the snow level stays above 2000feet. I know Horner used to train in the Auburn-Foresthill area. (45 minutes east of Sacramento) I get wet imagining the peleton going across the foresthill bridge