This will be a recurring point of contention here, and everywhere else for the foreseeable future.
I'll give my two cents again: Amtrak will not stray from the status quo. Single level equipment will alter the structure of trains too much. They'd have to lengthen countless platforms, change train layouts, and likely deal with longer, heavier trains. Personally, I think raising platforms for level boarding should be in the cards, but that'll be easier with lower boarding bi-levels. Plenty of stations around me (Green River, Helper) are already having their platforms raised slightly and what appear to be wheelchair ramps are being installed.
If not for age-related deterioration, the Superliners would stay in service indefinitely. Superliners are a tried and proven platform that works, Amtrak is hardly in a position to gamble the next 50 years on a new idea when what they have works just fine.
I'd bet my left leg Amtrak sticks to bilevel cars, the trade-offs are too risky.