I have often wondered why BOS-LGA and BOS-DCA have made sense as Shuttle routes but BOS-PHL has not. USAir operations on that route have seemed quite Shuttle-like, with high frequency hourly departures throughout day. For whatever reasons, USAir kept the BOS-PHL route as a separate (from the Shuttle), standard route.

In a post-merger world, with the combined company being tied (with B6) for the largest airline in BOS, do the economics or other characteristics of the BOS-PHL route change such that it might now make sense to convert it to be part of the Shuttle? If so, what change would that have in practice and would it be better or worse than the status quo?