VIA is gojng with the same accesible core concept as trsk. The only cars from the VIA order that would be really be out of place on Amtrak are the section sleepers and dome cars.
I could see cooperation on single level for the basic design and big picture items, but there would be differences in interiors, accommodation types, programming, etc. I don’t see Amtrak doing berths as an example. It wouldn’t be a carbon copy.
I mean, you could exclude the berth car (or swap out a roomette car design), and the dome could also be subbed for a reworked dining car to act as a lounge (sub a bar/kitchenette for the full kitchen?), but the point is that the underlying car could probably be the same down to the plumbing, at which point the differences are smaller than more than a few PV overhauls.
The domes would be an odd fit vs what Amtrak has done, but if you could find a way to have folks pass through step-free downstairs (I think that's the biggest issue if there are
any facilities on the "other" side of the train) and get one of those "elevator seats" alongside the stairs that a lot of folks have in their houses and get that waivered through, you'd be good.
I'll be honest - given the popularity in Europe of couchettes, I'm not 100% convinced that the berth car would be
totally without a business case. I think it would be touchier in the US, but at the same time I don't see it as a complete non-starter. It's really no less private than most of your airline lie-flats.
But at the same time, what's the difference between a berth car (for via) and a roomette car (for Amtrak)? Doors? Depending on the exact dimensions, etc., it might
literally be cheaper for Amtrak to just piggyback on the order and deal with that modification at Beech Grove, or to just order a bunch of shells to deal with in-house for your roomette sleepers. I'm not saying this is a
good idea, I'm just saying that (1) it might net out in their favor and (2) it would almost certainly be less troubled than trying to foist ADA compliance onto bilevel long-distance equipment.