I don't know if such a project would make any sense, but I it find interesting that several responses seem to think that the existence of many flights on the route are a negative.

I think that is a positive indication of a robust travel corridor, which might be an indicator of good possibilities for rail.

There were many flights (remember the various shuttles?) between Boston and NY and DC -- which is now a very good market for rail. Same could be said (on a smaller scale) for Seattle - Portland.