In Internet rumors we have this:
Rumor of the Week: The NBA in Bellevue
King County is lobbying to extend the hotel/motel tax to help Seattle pay for a revamped convention center in exchange for help bringing the NBA to Bellevue.
That is from Publicola.com, take it for what it is worth.
I am not sure why the Washington State Convention Center would need more money for their expansion. The Convention Center has control over the Seattle Hotel tax, was formed into a Public Facilities District last July.