Can Double Decker be self powered? I know Catenary ones can , like in Japan. Ive never heard of Double Decker 3rd Rail EMU's.
Can 30th Street Station support Superliners? I am guessing nit but if so then Silver Meteor can start at Newark instead of NYP and Lake Shore limited at Poughkeepsie.
Superliners will not fit through tunnels south of Baltimore, either, so all your long-distance trains would have to start in WAS.
This discussion seems to come up every few months (though, I swear, the last time we had this was much more recently than this). Really, there's nothing wrong with having two types/sizes of equipment in the LD fleet. There's nothing wrong with having single-level LD cars in the Amtrak system. The cost of changing infrastructure would be too great to allow standardizing. Any compromised car design would be a step back from either type of car that's out there now.
There's nothing "special" about a Superliner, other than its capacity. You can get the same capacity by adding cars. The current set of LD trains are nowhere near their maximum length. Current single-level LD trains, except for the Lake Shore, generally run with a baggage, two sleepers, two food cars, and four coaches (the Silver Meteor often runs with a third sleeper, and the Cardinal is much shorter). A couple decades ago, these trains ran 15-20 cars long.
It would be far, far easier to add a few cars to the train to get the capacity you want, than to invent a new long-distance car design that requires everybody to walk up and down stairs when moving from car to car (I know I said this already, in another thread very recently on this forum) just so that the train can serve high-level platforms. The "tri-level" type commuter car design already isn't designed with baggage storage (or enough restroom tank capacity) in mind. I've never been in the new NJT cars, but I'd imagine they're even shorter than the Bombardier-type coaches, meaning even less room for overhead luggage racks and such.
Turning those types of cars into long-distance passenger equipment really sounds more like a solution looking for a problem than anything else.
Update. Here's where the subject was discussed last time:
http://discuss.amtraktrains.com/index.php?/topic/33449-bombardier-bilevel-cars-over-longer-distances/