Not to be a pessimest, but I doubt there will be any future Seattle expansion. ANA and JAL surely won't fly into SEA from NRT, as the market is over-saturated with NW, AA, and UA offering daily flights, and KIX is being operated by a NW DC-10 which runs about 2/3rds full. HKG was a disaster for NW even before the Asian Flu hit (and was only operated 4X's/week), thus forcing the cancellation of that route. SQ and TG really have no large reasons to fly into SEA.
On a bright side, CX and KAL could be a possibility. KAL mainly for cargo purposes, but CX (if they did it right) could probably be profitable, just as long as they have AA to feed US Domestic flights (same as UA did in the 80's).