I did a little research on setting up automatic arm twists within Maya and had the idea to extract the x-rotation by using a NurbsSphere together with a ClosestPointOnSurfaceNode:
WHAT WE GET:
* this automatic twist calulation works within the range of -360 to 360 deg, without flipping.
* a locator parented under the hand ctrls is used as input for the closestPointOnSurface Node.
* the paramterV of the sphere (extracted by the closesPointOnSurface Node) is the basis of the twist calculation
* and an additional expression corrects the twist if necessary.
... if there is demand I could make a tutorial about this twist setup in the future.