I find it a bit odd the comments regarding the possibility of dining/lounge/cafe services on these cars, should Amtrak use these cars elsewhere.
The California Cars (Surfliner/Capitol/San Joaquins) both have two doors, located mid-car and at platform level, with ADA accessibility on the lower level. These trains offer a cafe service in a particular car - I believe on some trains the cafe happens to be on the upper level, on other trains it is on the lower level - dependent on the specific car type and the service (the Surfliner cars are different from the cars used on the northern serices.)
Likewise, with Amtrak's Superliner fleet - the dining car is on the upper level, but the cafe/lounge service area (including snack coaches) are on the lower level. The exception would be the "bar area" of the Empire Builder's coaches, and the Pacific Parlour car, where they are on the upper level. Regardless, access to either of these cars is NOT ADA-compliant.
The only western car design I know where access to the dining/lounge areas is ADA compliant is the Talgo set, because access to the cars from the first business coach, the dining/table car, the kitchen/lounge car, and the first "regular" coach, is entirely ADA compliant. However, the Talgo wouldn't work in this situation because it is not compatible with the higher platforms, nor does it have close to enough capacity.
What I could envision (for NJ Transit use), is a Starbucks type establishment in the lower level of a car, clearly identified so that those passengers who are disabled/handicapped and would like to use the services of that establishment can occupy the coach seating in that car. Periodically, the establishment can provide "at-seat" service, or a seat call button could be used to summon someone to take an order. The selection would be limited but could occupy a minimum amount of space, generate a lot of traffic and revenue, and requires very little investment.