Since they already have cities in UT and TX and don't think they'll do them again. My reasoning is that they appear to be spreading the love in red states and it may seem less ideological to only go to a nearby city such as Salt Lake City or San Antonio. This is also why I don't think they'll go to Portland or San Jose, but I could be wrong and they may decide to "go home" having completed cities in three red states. I could also be wrong if they are now moving away from ideology and to a more concrete business plan. If that is the case then Salt Lake City and San Antonio might make more sense financially.
My feeling is that they may move further East, but stay in red states. Any of the four are possible, but my guess is the next city will be either Nashville or Atlanta. I'm not counting Charlotte and Raleigh since they are in a more blue state.
I could be wrong since they specified Raleigh-Durham instead of simply stating Raleigh, and this also gives them more suburbs like their Kansas City operation.
Let's look at other tech companies...
Wow! Georgia gets 9% of page views from a fully electric car's browser. Atlanta may be Google's next move. It also is fairly red, has spread, and has a very big and connected airport to spread the word. Hmm.
I'm not counting out Nashville though. There's a very big music scene there. Does Google have any music media interests and plan an internet music service like Pandora, Spotify, or Amazon?
What do you think?