When Bruce Lee created Jeet Kune Do, I used styles that he had access to. One has to remember his philosophy on the martial arts in which there is no ultimate style. He used Tai Chi Chuan and Wing Chun as the base; then, he added moves and techniques from: Tae Kwon Do, Boxing, Epee Fencing, etc.
Bruce Lee wanted to add Muay Thai moves into JKD; but, the style wasn't available to him. But, he was able to add the hardcore mindset of the Muay Thai fighter. In today's MMA bouts, he'd probably lose matches; but, he'd have access to so many different styles at the same time. MMA would actually motivate him to improve his JKD.