A long time ago -- circa 1989-1990 -- Yamaha made a few keyboards called the X4500, PSR-4500, and PSR-4600. I think all three were basically the same but with a different color scheme. But one of their unique features was that, instead of pitch and mod wheels to the left of the keyboard, they accomplished these functions with wide roller bars in front of the keys -- and by in front, I mean closer to the player, so that they could be operated by the palm of the hand while playing. I suppose they could also be operated by thumb, as well, if desired. While this might seem like an expressive way to control these functions without having to take your fingers off the keys, it obviously never caught on.
I never had any direct experience with these keyboards, but they seemed like they were pretty "far out" for the time. I think they even combined AWM and FM synthesis, though I believe they only had 8 note maximum polyphony. If I ever found one for a good price, I think it would be cool just to play around with it to see what it could do. There was also a more basic X3500, but I think it still had the roller bars.