EVERYONE
THIS IS AMAZING!!!

I was playing around with my python implementation of .j2l files and surreptitiously adding what I thought were new features, and then it occurred to me to check if JJ2 actually had them already... and it DOES. JJ2 (but not JCS, of course) lets you use flipped tiles and other animations for animated tile frames.

MIND: BLOWN.
(my earlier attempt to change the order of the layers through the .j2l file was, unfortunately, unsuccessful.)
(also it doesn't work in TSF; you'd need different values)

ETA: I am trying to get it to work in TSF but I think j2ff doesn't support it, so I need to roll my own; be patient.
ETA2: Here's another 1.23-style example for cooba, showing that, in combination with belts and Reworder, working electric barriers can indeed be made. Uses Newspaz's Tubelectric conversion.