Boston-Brazil will probably never happen. I think it's time we put that one to bed. In much the same way that many European routes from the West Coast, even if the traffic is there, don't stand much of a chance of operating successfully (San Francisco-Rome comes to mind), it's a long route with low yields and there are a half-dozen viable hubs in between that work perfectly well funnelling traffic.
Furthermore, it will NOT be a US airline flying it. I give the biggest odds of the route ever being served to TAM. However, I'm still doubtful that Boston - South America (outside Brazil) is big enough, combined with Brazil traffic, to warrant a flight to TAMs hub in Sao Paulo; not when there's New York, Washington, Atlanta, Miami and, to a lesser extent, Dallas and Houston in between. Hell, even Charlotte has a flight to Rio and soon a flight to Sao Paulo.
Here's a few major South American cities outside Brazil with over 10 people travelling per day from Boston that could theoretically (though not necessarily practically) use GRU as a connecting point:
- Santiago: 14 pdew (contracting)
- Buenos Aires: 23 pdew (growing)
- Lima: 20 pdew (contracting)
There's probably a half-dozen other markets, like Concepción, Chile; Córdoba, Argentina; La Paz, Bolivia; Montevideo, Uruguay; and Asunsión, Paraguay that have under ten that could theoretically help to fill a TAM plane from GRU to BOS. Though, again, yields are not strong enough to support a nearly 5,000-mile flight and several of those cities are served by American nonstop from Miami. Even if Brazil is the "big enchilada" out of Boston, almost all second-tier cities in Brazil, with the arguable exceptions of Belem and Natal, are served from Miami by TAM and American, a soon-to-be partner of TAM.