Update: Nearly 2 months later, Alaska still has that notice on its website.

I booked the flights with Chase Sapphire points and called HU directly to upgrade seats to extra legroom for $110 each way. A few days later they called me back to say that they had changed the configuration of their return flight -- it's still a 787-9 but this version has no extra legroom seats. They refunded the $110 for that leg after politely rebuffing my suggestion to put me in business class at that fare. They actually still have 2 rows on that flight with extra legroom. One is the 1st row of economy and is booked (but I'm monitoring for changes). The other is an exit row further back, but Chinese airlines are not allowed to seat pax over the age of 65 in exit rows. More than half the seats are as yet unassigned so I'm hoping at least the seat between the 2 of us will remain empty.