I just booked Acela first tickets for Feb 19 and 20. Usual process for Feb 19. But for the Feb 20 ticket, the system assigned me a specific seat, and then offered the opportunity to change it, using a clickable seat map.
So I'm guessing Feb 20 is the first day this is possible?
It looks like for those who book early, the "rush" to get a good seat is over! THANK YOU AMTRAK for finally making this work.
EDITED TO ADD.... from amtrak.com:
Assigned Seating Exclusively Available on Select Acela Express Trains
You can now reserve your preferred seat in First Class on select Acela Express trains. Have more piece of mind knowing your seat is waiting for you. Once you've selected Complete Purchase, you'll automatically be assigned a seat. To select a different seat, use the Amtrak app or visit Amtrak.com.
So it looks like it's only on some trains. Hmmmm... hope this is eventually a system-wide rollout.