Though there may have been others who inspired him, the earliest version of a DTP type of program in my experience was Clif Taylor, and his GLM Method (Graduated Length Method) back in the very early 70's.
He believed that if skiers could learn a parallel turn on very short skis, and then gradually lengthen the skis as their experience/ skills developed, they would never be caught in the wedge/wedge christie/stem christie zone.
But like many great programs, the first phases proved beneficial, but then rather than continue to lengthen the skis, most skiers stopped at what was then considered a short ski. (by todays standards, they were probably average) Through the mid-late 70's, there became a controversy about what short skis did to the snow, shape of bumps, etc. The racers still swore by long skis, and freestylers were on the short ski side of the argument.
As time went on, both sides moderated their stances a little, and everyone did accept that learning on shorter skis was of benefit. At the same time, it was agreed that a longer ski provided performance a short ski could not match.
But in retrospect, like many other technological advances and teaching concepts which were dismissed before fully developed, they were far ahead of their time.
The last I believe I heard, Clif Taylor was selling real estate in Aspen.