Texas would be a good choice too, possibly better than California due to the lack of mountain ranges, and shorter distances between the major cities. I think the only reason SF-LA is being talked about more seriously than Houston-Austin-Dallas is the relative political climate in the two states. But even given that, there was a serious initiative to build a line in Texas in the late 1980s/early 1990s, killed in part by Southwest Airlines' aggressive lobbying.