Twist like SimplerDeform but with bones? I want to create the same sort of twist that you get from the SimpleDeform modifier, but by using an armature so that I can have more control of it. I want to get at least 360degrees of twist, maybe up to 720. The object is basically a cylinder.

If I use just a couple of bones, then when they twist, they pinch to no thickness in the middle. What is the proper setup with bones to get the amount of twist I want?
I would try to use a bendy bone with controllers (see here), then add a bone at the base of the bendy bone (I'll call it "rotator" from now on). The opposite bendy bone's controller will be parented to the rotator, and its rotations will also be driven by the rotator.

In theory, this will make the opposite controller rotate arround the bendy bone base and rotate it twice the amount of the rotator's rotation. The bendy bone would form a perfect half-circle shape, without any wrong deformation.

Duplicate the whole thing and invert it to get the other half, and you have your simple-deform-like rig.

I did a test, you can download and retro-engineer it.