This is still an issue, it seems. I have been struggling to book J itineraries whose first (maybe last too?) leg has no J cabin. e.g. if a city is served by both A320 and Q400, only itineraries with the A320 show up for J. Given a not insignificant number of routes are J-less, this has become quite annoying. I actually ended up booking via UA (with codeshare on first leg, and UA on second, even when I prefer AC) because I can actually book the dang thing.

This seems seriously nuts: how much money is AC leaving on the table here. I've never flown UA as much as I have this year due to this problem.