I don't see air travel and train travel competing on this route. Flying up to JFK/LGA is great for connecting flights, but not for going into the city. Going out to DCA (or heaven forbid, IAD or BWI) only to fly to LGA/JFK/EWR and have to take a train or taxi back into the city is a very circuitous route.

If Musk's plan comes to pass, I'm seeing it as an Amtrak competitor. But like you mentioned, price is almost everything.