American already has rights to fly JFK-NRT, as well as BOS-NRT. The only reason that they don't is that they have been unable to obtain slots at Narita. They were awarded route authority after the last round of US-Japan aviation talks when the market was somewhat liberalized. Following is an excerpt from a press release
issued by American on March 17, 1998...
We applaud DOT's plans to award new U.S.-Japan routes as soon as possible so the competitive benefits of the new bilateral can be realized. In addition to starting Chicago-Tokyo service on May 1, we plan to begin new New York Kennedy-Tokyo, Boston-Tokyo and Dallas/Fort Worth-Osaka service by November 1, and today's action paves the way for that new service to start."
American retains rights for the routes, and intends to begin service as soon as slots are obtained.