Spotted this flight while trawling through the AA timetable:

AA 297 SJU-HNL Dep daily, B763, 5886 miles.

This flight stops twice in MIA and LAX, but with the same flight number. It is, I think, the longest domestic flight in the OW system. Note, there is no HNL-SJU return flight with a single number.

Anyway, it might be helpful for those wanting to maximize miles, but also travel N.America-Hawaii-SW Pacific.