I have returned from my trip and thought I would post an update. I'd fly JX again, which is probably the important bottom-line, but I added more details below to help others make up their minds.

I did indeed wake up at 00:50 Pacific time and called Starlux Taiwan office to get a seat assignment for the outbound flight. The agent gave me a seat of my requested type, and informed me that an enhancement had been deployed, and I should be able to request seat assignment via "My Trip", though the 48-hours before departure limitation still exists. This was a big help to me personally, because the flight times were not really conducive to calling due to non-24H operation of JX reservation center, calling meant at least a 10-minutes wait on hold each time before speaking to an agent, plus I like being able to see the seat map while making my seat selection. I was lucky and both flights were not very full, so I was able to get the seat type of my choice despite selecting them between 40 and 48 hours before departure.

Through "My Trip" I was also able to request a meal, even though I was just choosing from one of the two options that would be offered later, and not getting a special meal type. Pre-selecting a meal resulted in getting my meal delivered a little bit earlier than others which was nice, as I like to finish the meal ASAP and then attempt to sleep.

I flew on 58506 on the outbound, and 58504 on the return. The planes were in good condition, as expected of essentially new equipment. I really like the seatback design of the Recaro seats. The doubled-over tray table opens up a space above it for a storage cubby and cup holder, which I found quite useful. Seat comfort is OK, and pitch is decent. As is common for airplane seats with IFE, there is an electronics box which impacts foot-well space. IFE selection was decent, I found something to watch for the limited time which I used the screen - I tend to prioritize trying to sleep on the flights due to having many hours of tasks to do post-arrival.

The FAs were great, both kind and diligent. The meals were so-so, I was not impressed by the special restaurant co-branded meal on my ex-TPE flight. Ground operations was quite efficient - my checked bag was out on the carousel by the time I had passed through immigration in Taiwan, and I only waited about 25 minutes for my bag at SFO after passing through Global Entry. It's not uncommon for me to wait 40 to 60 minutes for my bag at SFO with an EVA flight. JX provided an amenity kit (eye mask, socks, tooth brush/paste, ear plugs), as well as slippers, small pillow, blanket, and bottle of water at each seat (even in economy, where I was). All of these were positive, and did make JX feel like a better airline than average.

RDMs posted quickly to my AS account, but the EQMs did not. I called AS, waited for more than an hour on hold, and then spoke to an agent. She said an internal team needs to look into the issue, and I would get an email update in a few days. I received an email less than 24 hours later and my EQMs posted. So I am happy with the service from AS too (and I am a new AS customer, moving my business over as result of AS purchasing HA).