Philly to Pittsburgh is longer than DC to NYC, or most of the ridership of the Acela put together, wouldn't serve all that many people, and would be at least a 4.5 hour trip even with the unlikely assumption that you'd get Acela's average speed for the whole trip.
I'm also not sure what building out NE service does to make Chicago more accessible. Chicago is prohibitively far from all of the east coast cities to make NE rail meaningful.