Officer (Captain?) West Point, Amtrak's A-Day to Date experience with Diesel self-propelled equipment, or otherwise DMU in newspeak, has been one to forget.
The "rebuilt from the ground up" Budd RDC's Amtrak acquired for the Black Hawk (Chi-Dubuque) were nothing but a mechanical nightmare and were withdrawn after two years of that train's six year life. The "hand me downs" from the PC, including the NH's "Roger Williams" set, assigned New Haven Springfield, were also reportedly nightmares (BTW, I speak first hand regarding the Black Hawk).
The final straw were the likely only "duds" that Budd ever built - and those were the SPV-2000's, or otherwise a self-propelled Amfleet. Their intended assignment was Springfield-Wash where at New Haven, they were coupled to a Corridor train, thence "dragged" the 316 miles to Wash. I cannot recall the exact dates they were in that intended service, but they flopped and apparently Connecticut bailed them out finding some CDOT routes to live out something resembling a normal service life.
So with this history in mind, I doubt if Amtrak is looking for a redux.
Finally, lest one think "I'm hypocritical" with my comments over at the METRA Forum, where I hold that METRA's pre-COVID ridership is simply never coming back and I'm suggesting they replace their some-50yo with overseas sourced DMU equipment for their off-peak services, a passenger would be on one of such for, maybe, twenty miles. I've ridden such overseas and the engine noise in the Stadler cars is less objectionable than I found the RDC's to be (full disclosure; that ride was Salzburg to Freilassing - all of ten klicks).