Knee-High boots disappeared from retail shelves for the same reasons that ski length/side cut is now being looked at by the FIS - namely injuries. It hard to grow or sustain a sport, which is dependant on large numbers of participants, when the equipment required to participate is viewed as inherently dangerous.
Rear entry boots like conventional skis work well for some and you can still see some folks skiing in them. Rear Entry boots were slop buckets for many and they were never widely embraced within racing circles or by most other expert skiers for that matter. They ultimately proved an innovation failure.
GLM worked only as long as skiers stayed on short skis. They tended to be very squirrelly at speeds much above those that novice skiers attained.I suppose that had to do with the design constraints of the time. Cliff Taylor is long gone from the scene and so is the movement he founded.
I am not disparaging innovation by any means. I'm just suggesting that the jury is still out on the optimal side cut/length per category of ski given existing technology and other considerations at this period of time. Last season many were predicting that mens slalom skis would move from 155cm down to 150cm this season. Instead they are headed somewhat in the other direction to 165cm. Retail ski trends could move towards longer and/or straighter-or maybe not.
I do not suggest that we will find ski manufacturers sandblasting the graphics off mid-1990's skis although some might if they really thought they could get away with it.