You'd have to think they have thought about and bypassed SEA-SLC a billion times over the years. It's the one city in the west that AS doesn't serve.
There should be an opportunity in SJC but countless airlines have found SJC to be an oddly low-yield city for reasons I cannot figure out. The higher costs now that the city has to pay for another new terminal can't help.
SAN - somewhere is a good bet - lots of cities can use a direct flight to SAN.