I very much encourage every American cyclist who has dropped the coin for a coupler or 'rinko' bike to take just a minute and a half to contact Adventure Cycling Association...

https://www.adventurecycling.org/advocacy/train-travel/

"We know how hard it can be to travel with your bike on Amtrak and we want to hear what issues are important to you. "

...explain the issue and work on getting a written policy/letter from Amtrak ok'ing any bike packed into 34" x 15" x 48" (860 x 380 x 1120 mm) for carry-on.

A rogue conductor might argue with you, but I have a suspicion they won't argue with a letter from Secretary of Transportation Buttigieg.

Fun fact: Adventure Cycling claimed to have been the driving force behind more bike space on Amtrak's refreshed/updated rolling stock on the Vermonter, Northeast Regional routes, the Keystone Service, Downeaster, and Hartford Line routes.