I haven't seen anything posted on this and I didn't follow the AC-9s when they came out.
But, apparently, the AC-9s would not lash up with other Legacy locomotives, as evidenced by this video and the comments beginning around the 1:21 mark in this video: https://www.youtube.com/watch?v=_0DBVSqRoPI (Whether you chose to believe this explanation is up to you......)
So, riddle me this, Bat Man: Both the AC-9 and the recent release of VL Challengers are articulated steam engines that Big Orange has apparently seen fit to remove the articulated sounds from and have both drivers "in sync" all the time.
What are the odds that the exact same technology and programming that is in the new VL Challengers is the same that are in the AC-9s.....and now the Challengers won't lash up with other Challengers, Big Boys, or FEFs?
Has anyone tried this?