Try to think about this through Amazon's lens. What does Amazon NEED?
NEED
They need LOTS of tech people, and QUICKLY. What cities have that? Not Detroit
They need to be able to RECRUIT to areas that will draw talent (whether you like Seattle or not, you can argue its an acquired taste -- costly and not sunny)
They need LOTS of space and they need to be able to scale quickly
They need something this new location can offer that dreary Seattle cannot (Sun and lower cost of living)
WANT
Amazon would love to get massive tax credits
Amazon would love to get cheap talent right out of school.
So given this criteria, I believe Dallas, Austin, North Carolina, Denver, Orlando would be likely targets.
BONUS FOR AUSTIN: Amazon just bought Whole Foods. I used to live in Austin and so I know Whole Foods holds leases on EMPTY office space all over downtown.
Detroit is bad for recruiting
Chicago is not great for tech
THINK like Amazon and you will win.