Today I heard this from a check airman.
We are getting 12 777-300's.
The announcement is within the next two weeks.
The simulators and manuals are being readied for the differences between the 777-200 and 777-300.
I, too, have heard from multiple people that this is, indeed, happening, and that an official announcement is, indeed, imminent. Getting -300s from JAL is questionable, though, since JAL only operates 7 -300s and 13 -300ERs, so if AA were to take 12 of anything, there wouldn't be enough -300s at JAL, and taking 12 -300ERs would wipe out JAL's entire premium longhaul fleet, which I don't see happening. I could foresee these -300ERs showing up on DFW-NRT, DFW-GRU, MIA-EZE, and maybe a few other dense routes, plus used for new growth markets currently outside the reach of AA's existing -200ERs, like MIA-JNB or DFW-HKG. Will be interesting to see ...
JFK-NRT is being moved to MIA...hence the need for 777-300's.
JFK-HND is doing poorly on sales and a decision will be made if this flight will be long term.
I have been hearing something to this effect for months - JFK losing a few flights per week, which would get shifted down to MIA-NRT. However, it sounds like what you heard was that JFK was losing its AA flight to NRT altogether?
MIA getting a nonstop link to NRT/Asia is not surprising - if well timed (I'd guess a roughly 1000 MIA departure and roughly 1900 MIA arrival) for Latin America, the flight should do quite well. However, as others have said, if the -300 rumor is, indeed, true, and MIA is, indeed, a driver of those aircraft, than it would need to be a -300ER, since a standard -300 couldn't do it without a severe penalty. Then again, they could operate MIA-NRT with the existing -200ERs, albeit with a smaller (relative to a -300) penalty.
As for JFK, the now-combined AA-JAL schedule doesn't really need 14 weekly flights JFK-NRT plus 7 JFK-HND. It's overkill. A daily JAL 777-300ER plus maybe 3-4x weekly AA 777 is probably enough. JFK-HND was doomed from the start. The schedule is absolutely awful, and I don't expect it to be around for long. It's really just a total waste of 1.5-2 good 777s worth of capacity that could be so much better utilized on, say, DFW-ICN or even ORD-DXB.