If AA/JL wanted to add a JFK-NRT flight, there is nothing stopping them from adding it tomorrow, right? So I can't imagine that is the end game.

And I'd think if there was a NRT flight between the 2 carriers, it's more likely that it's AA operated. NRT traffic would be less premium and for connections. Quite honestly that is a better fit for the AA brand vs JL. They are still competing with ANA with 2x/daily JFK-HND and if AA/JL split the frequency they might lose passengers to ANA.

I think AA would run a 772 vs 773 largely because how can AA offer F on this route when they have a JV with JL and the difference between AA and JL F would be so massive. At least until AA F is eliminated