Southern California?
If we assume that future "shuttles" couldn't handle narrow azimuths and such from a place like Texas, I'd be interested to know why launches couldn't be done reasonably efficiently from Southern California towards the Pacific. The weather's comparatively mild out there. I am unfamiliar with Vandenberg, but it's not that much more North of Cape Canaveral. And from what I read, a launch from Cape Canaveral vs. a launch all the way down from the equator is only 20% more inefficient (fuel-wise).
All the while, though, the Europeans and perhaps even the Russians may be launching their folks from Guiana, South America...