and with rumors of WN doing things like PHL-BOS and BOS-LGA and BOS-BWI, it's going to quite a battle with WN.
Although they have not announced their schedule, so your guess is as good as mine, I doubt you'll see WN fly from BOS to LGA. They would be competing with jetBlue (to JFK) and Amtrak for the market to which they cater.
And between BOS and PHL, there are already a million seats a day, and any more flights between those cities would just water down the fares even more. And unlike most airline managements, the people who run WN aren't stupid.
I also think it unlikely that WN would fly from congested airport to congested airport. That would be deviating even farther from their business plan. Route an airplane between BOS and LGA, or BOS and PHL, during a snowstorm or on a thunderstorm day, and you lose that airplane for most of the day.
Besides, the majority of the people riding US from BOS to PHL,
aren't going to PHL. They are connecting to go someplace else, and are only going through PHL because they were practically
given the fare on the Internet to keep them from flying non-stop to wherever they're going on a
real airline.
So it would figure that WN would go after
those customers, flying them from BOS and LGA to wherever it is they actually want to go, for a reasonable fare that still makes money for the airline.
BWI? That's more likely, as a means to siphon off BOS-DCA traffic, and to connect passengers to other WN flights from BWI to points not served non-stop from BOS.