I'm afraid Amtrak will never return dining cars to its east coast service. A trip from Washington to Boston is about 8 hours and 20 minutes and on the Acela about 6 hours. They could serve boxed meals at the snack bar with a hamburger or something like that but that is all we will get.
Dining cars are very expensive as they produce no actual revenue. However, a car full of passengers does produce revenue.
The new Acela will be 10 cars rather than 8 as in the present Acela. That means about 12 percent more passengers. The Acela already makes a profit so the new ones should be even more profitable.