Terminal E - Logan's only international terminal, is bursting at the seams. 17 airlines are crammed into a small facility - one Massport's now updating. The terminal's also plagued with antiquated jetbridges that too frequently break down causing arrival delays.
As many as five years ago, several airlines, including AA, were trying to gain approval to add customs/immigration facilities at Logan's other terminals thus spreading the load of international flights, but I don't know what's happening with that these days.
As for the newer Airbus's and bigger 747's, perhaps the ramp areas around Terminal E are too congested to accomodate them. Wide open spaces are a rarity in Boston, and Logan's no exception. Perhaps when Terminal E is finally expanded, we'll begin to see some A-340-600's and 747-400's landing at BOS. Do ya think they'll design special gates to accomodate those new A-380's? Heh heh