My view is that probably all of the factors mentioned in the original post played their part.
i.e.
NS Dance has evolved from other styles of dancing. Seeing Soul Artistes dancing and performing elaborate moves, live or on screen, had a great influence in the direction the style of dance evolved. The ability of some dancers to embellish their moves may have been due to the stretching and high kicks that they practised in their Kung Fu or Karate classes which were around certainly before '68 when I first took them up. (Maybe those that sought something different out of life applied this to 'sport' as much as music). The fact that NS and Martial Arts simultaneously enjoyed a certain popularity in the early 70's is a mere coincidence, but a fortunate one for those that had the energy to be involved in both.
- Kev.