JAL's been at 84% according to the Globe article choo mentioned. As long as that load factor is evenly distributed between the front and back of the plane I'd say they're ok, but if it's disproportionately skewed towards the back, that's a problem.
Here's the portion of the article discussing Logan and future flights.
Massport is in the beginning stages of developing a long-term plan to address challenges such as passenger growth at Logan, which hit a record 28.9 million last year. Logan’s newest international route, the Japan Airlines flight between Boston and Tokyo, has been a success since it launched in April, with daily flights running about 84 percent full.
Glynn said he is focused on adding more nonstop connections to overseas markets in Asia, Latin America, and the Middle East, including Israel and the Persian Gulf, all regions with significant or growing business connections to Massachusetts. Central America is seen as a prime contender for the next international route.
Logan’s relatively small size, however, poses a challenge to attracting new airlines and routes. There is little room to grow because the airport is surrounded by water on three sides and the dense East Boston neighborhood on the other. No other airport serves as many passengers on such a small footprint — about 1,700 acres — according to Massport.
The terminal with the most potential for expanded service is international Terminal E, which is only busy when European flights come and go in the afternoon and early evening. That leaves room for flights to and from Asia and Latin America, which operate at different times.
“Boston and Massachusetts are part of the global economy more so than many other cities, but we have a small campus to work with,” Glynn said.
http://bostonglobe.com/business/201...-challenges/klXxCD840yoBHJnUzZKffM/story.html