The bus has 50 seats, and standing room for maybe 20-25. This includes having 1-2 people standing unsafely on the swivel plate in the middle of the bus.
One of the issues in general with increasing Seattle-Bellevue throughput is having to bridge the lake. I-90 traded a separate bridge of dedicated express lanes, for HOV lanes combined with other traffic - so the under construction Link light rail can use that separate bridge. 520 is another option, but there's a toll since they just replaced the narrow 2-lane pontoon bridge with 4-lane highway that's suspended higher above the water.