I'll finish up my current DONE3 in the next couple of months, and planning the next one to start immediately thereafter. Is DFW/ANC the longest possible segment within North America? Years ago there was a LAX/MBJ flight, -- in addition to it being quite long, MBJ was not on the list of transcon exclusion cities, so I used to do it several times consecutively within a single itinerary.

Your 'in the next couple of months' might be the rub here. Alaska supposedly flies ANC-JFK on a seasonal basis but ... when does that season start?

The AS service from SEA to LIR (Liberia in Costa Rica) is only 65 miles short of the JFK-ANC service, and doesn't use up a transcontinental flight.

Good point. Although just to be clear, JFK-ANC is not transcon either.

Thanks for the info, friends. I'll try to build in JFK/ANC. Again, thank you.

The FlightConnections website (which I don't find entirely accurate for a number of reasons, including the fact it's had Oman Air listed as part of oneworld for several months now) says ANC-JFK is only June to August.

DFW-HNL (3288 nm)?

12JUN25~19AUG25, daily

But I think xONEx has restrictions when it comes to Hawaii flight. I believe it has to be Asia - Hawaii - Contiguous US or vice versa. Maybe others can confirm.

Correct. Rule 4(b): "Backtracking between Hawaii and other points in North America is not permitted."

Unfortunately yes you then need to continue to Sydney or Japan (believe these are the only oneworld flights out of HNL) -> I would however observe that this route (which I'll take for the second time in a month on a DONEx) is more pleasant as you have a long haul plane and service, including access to the Flagship lounge. And if collecting segment based earnings (alas for me, now gone due to the BA changes) it is 2x what you'd normally get on, for example, DFW to NRT.

So your ideal route would be something like this for your six segments (think this would work?), where XXX is as far away as avoiding the trans-continent restrictions:
JFK-LAX (transcontinental), LAX-XXX-DFW-ANC-DFW, DFW - HNL

Even better if you can route the opposite way, as JFK-XXX-DFW would give you a lot longer flight options than from California per this table:

Oneworld Explorer restrictions across the continent

There are also the 'trans-con' AS flights that are not on the list, LAX-NAS, LAX-SJO, SEA-CUN all over 2500 miles. I would not expect AS to have any D space on the JFK-ANC flight. When I checked that flight last year, it was a random D1 on very few days.
Last year I flew JFK-LAX-NAS-LAX-ORD-ANC-DFW. I doubt that one can earn much more in the miles category.

I concur. I search throughout the summer season to no avail. I was looking for 2 D fares.

For the benefit of future readers, additional options should become available when HA joins OneWorld. For example, HNL-BOS at 5,095 miles may be the longest domestic route, though this would not be so useful for xONEx as mentioned above.

True, but NRT-HNL-BOS is 8,914 BIS miles, and NRT-BOS is 6,701. The difference is only a little less than BOS/LAX, so you essentially pick up another transcon at the cost of one segment. I'll definitely consider it depending on how it fits in to the rest of the itinerary. Thanks for the idea!