Nothing big in Seattle besides MSFT and AMZN, and MSFT is in long term decline.
Come to think about it, I don't think Seattle can rival the breath and depth of Bay Area, ever.
Our biggest challenger will come from China. Speaking of Bay Area there is a new Bay Area: the Guangdong Bay Area, that has 9 cities in the Pearl river delta, including heavy weights like Shenzhen, Guangzhou and Hong Kong. It's the new buzzword when I was in Hong Kong. And they explicitly mentioned the San Francisco Bay Area as competitor.