I'm going to go ahead and throw this post out there as something to come back to as I experiment. I've been trying to find a unique solution for creating a bendy limb rig. I'm shooting for something similar to Christopher Crouzet's rig, which I mentioned here. I want something to create and maintain a smooth tangent curve over the length of the limb (let's say leg in this case), instead of multiple secondary controls for each span of the leg. Overall I'm envisioning this constant curve over the length of the leg, then an additional layer of control below that, where its applied to the upper and lower portions of the leg, and if its not overkill, an additional layer with two of these per span of the leg.
I'm playing now with creating a curve and utilizing tangent constraints on the joints. I want to try to find a smooth way to manipulate the curve. So, we'll see what happens.