This would also avoid the political problem that a split fleet causes - Amtrak can't just go out and order 200 cars right now and hope to use them throughout the system, and any given order is "somebody else's equipment".
I mean, at some point the combined hassle and the added cost to run shorter trains due to the quirks of the bilevel equipment means that Amtrak might be better off just planning to lengthen platforms at a number of stations, and at the rest they're already double-spotting so managing that via seat allocations might make more sense. Also, for breaking even on capacity you really only go from something like eight or nine cars to eleven or twelve - basically, an extra coach, an extra sleeper, and possibly one other service car.
Frankly, if Amtrak could throw around 1000-1500 cars [1] onto the back of the VIA order I'd say they should just go for it and write off this whole thing as a misadventure.
[1] A 3:2 ratio of Superliners to single-level equipment would put the Superliner replacement order around 720 cars. You have 180 Viewliner I/II cars and then you have 145 Amfleet IIs. Yes, some Superliners are in state service, and yes I presume the Auto Train would get its own replacements. But a straight 1:1 replacement of the fleet is essentially 1000-1100 cars. Amtrak has some explicit expansion plans they've been pressured on (e.g. Daily Cardinal, Daily Sunset, Sunset East), and there's probably unmet demand that could justify lengthening some trains by a few cars above the above numbers, so guessing at up to 400 additional cars seems realistic.
