Theory and practice inform each other in a dialectic relationship all the time. An example --> modal jazz was born out of an intellectual/theoretical realisation that functional harmony had hit an end point with be bop. Some new rules/dogmas/conventions were formulated and a whole new field of improvisational jazz was opened up. Subsequently, new theory arose from this new music.
What was the main driver for musical innovation in the 20th century? Within popular music, new instruments and new technology were probably most important. The electric guitar, distortion, multi track recordi