This breaks mechanics and designs that I use in many places.

It fixes a bug you relied upon where pistons push things that aren't even in front of them, yes.

https://xkcd.com/1172/

This was done to keep a feature: #367 (comment)

That "bug" is what makes practical piston elevators and piston-bolts possible with mesecons, as well as reasonably moving carts around.

This was done to keep a feature: #367 (comment)

I can certainly attempt to re-add it in the +Y direction (so that objects on top slide with while objects that are just next to the stack don't) if you think there is interest in that. I'm not sure this is all that realistic given the instant nature of the movement - inertia would keep anything resting on top in place - but I suppose realism isn't always the goal here.

Another possibility would be to use a smaller radius for players than for other objects - this would still fix the original bug as reported, where players get pulled with a stack (and into a node if present), without removing the buggy behavior for other objects if this is what is desired. If there is any support for this, I'll either modify this PR or close it and create a new one as appropriate.

That "bug" is what makes practical piston elevators and piston-bolts possible with mesecons, as well as reasonably moving carts around.

I have no idea what a "piston-bolt" is, but there are certainly piston elevator designs that do not rely on bugs. I've even shown you one of those on VE-Creative (and you seem to like nocontroller challenges, how about a nocontroller version of that one?)
I also fail to see how moving carts around in the way you have shown is anything but a bug - carts are supposed to be on rails, not shoved off to the side at random.