As for the JFJKD kick link - I think (but don't exactly know) that the particular sidekick made so popular by Lee is a modified WC sidekick. The chambering, leaning back and hip motion came from who-knows-where, but the heel thrust and footwork are exactly like the WC version when it's used with footwork or when closing the distance. You can even cross-step to cover more ground (sure you all know that).
That kick looks exactly like a chasse lateral median from savate. The chambering, the body position, the mechanics of the kick, all of it. So I assume [given Tao of JKD, etc.] that savate is a possible or even probable source for the kick. Although savate footwork doesn't tend to involve that sort of footwork as much [although cross steps and 'skips' are used sometimes to close distance quickly].
But as you say, who knows, there's a lot of technique convergence across styles.