I just created what may be the first laterally articulated ski boot! After major surgery on the cuff of a very very old pair of lange 4 buckle recreational boots I now have one right boot where the sole can be inclined about 5 degree onto either edge with only ankle eversion/inversion. the side rivits for the cuff were removed, and I fastened to cuff to the lower boot at a pivolt point just above the heel. with several other changes to shape different parts of the shell and create a pivot point in the front, I was able to get a working prototype.
The first thing I notice is that there isn't that much difference when you first put the boot on. it still feels pretty firm side to side, maybe a little more movement range. But then when I start setting the boot on edge I find it is much easier to set it to a very sharp edge angle without torquing my knee. It feels much more comfortable and controlled to set the boot on edge. support leaning backwards is about the same, but I had to add some forward flex because the design is so crude. I have certainly seen "soft" boots with more forward flex.
So I can't wait to ski on these boots! one is unmodified for comparison. I hope to try them tomorrow and report back here.