Today's UA flight from IAD to HND has 2 more open J seats after everyone on the waitlist using MUA or PP cleared (20 people).
This is tomorrow's flight to HND. 26 J seats booked, 50 total available. Only 6 on the waitlist too.
I think demand for Japan has fallen off a cliff post-summer and economy fares on other airlines are reflecting it but hopefully United's J pricing reflects it soon too.