The shrinking/disappearing PE cabin probably also has something to do with codeshare and how much the airline partners are willing to pay. Since none of the Taiwanese airlines are in any sort deep metal neutral codeshare/profit sharing relationship, they have to manage the seat inventory in a way that doesn't end up being a free upgrade for someone. It's easier to just eliminate it especially if the the simple codeshare involves both short haul and long haul segments.

JX's relationship with AS is probably one of convenience for both parties. AS is really the only one that can do feed and non-alliance onward connection on the West Coast which is why AS has a lot of non-alliance codeshare and interline relationships (e.g. SQ). So I wouldn't read too much into whether that means JX is primed for OW entry... it's just too early for them (and OW) to think about it.