Is it correct to assume a Texas resident may order one from another dealer and drive it home? Can they just drive it home and legally have it registered in Texas?
Yeah, you basically just order it online and there's no problem. There are a couple of showrooms in Austin and from what I've heard, although you can't actually purchase it from the Tesla showroom, you are welcome to use their kiosks to order one via the internet.
That's basically what Tesla already does, although they'll ship it so you don't have to drive it from the factory.