I will answer this by referencing an interesting stat about
UA mentioned on
FT a while back:
SFO only has a couple Asian destinations (it was 1 then, and maybe 2 or 3 now) that
ORD doesn't also serve N/S. In other words, I think this is a reflection of overflying/bypassing the West Coast hubs to Asia.
As you mention, West Coast U.S.-Asia will always be king for O&D, and as such airlines will be happy to take on connecting pax to help fill it up and reduce CASM. But yes the percentage of non-backtracking connections over West Coast hubs to Asia will continue to decline (flying
BOI-
ORD-
NRT doesn't make sense vs.
BOI-
SFO-
NRT). Also don't forget 787s and 350s which will begin opening up even more n/s East Coast/Eastern U.S. to Asia routes, further reducing the proportion going to West Coast hubs.
If anything, I'd argue the biggest shift will be the last one -- from West Coast as the primary gateway until the last decade or so, to most of the important routes flown n/s from
ORD/
JFK/
EWR/
IAD/
DTW/
ATL/etc. Those Midwest and Western hubs will both lose a bit as traffic inevitably shifts to those nonstops flying out of East Coast hubs going forward, but they will survive from incremental connections (e.g., those who don't want to backtrack for
CVG-
EWR-xxx and instead want to stick with
CVG-
ORD/
DEN/
LAX-xxx) and their O&D markets.
Don't get me wrong -- East Coast to Asia and West Coast to Europe will always be relatively smaller than the near coasts across the oceans -- but you are correct that the landscape is and will continue to shift away from West Coast Asian gateways. Offhand I'd guess that increased overall pax travel will probably mean that those West Coast hubs don't really see too much net drop in traffic in the long run either.