Is a monobloc variable incidence wing viable (updated)?
Yes it is a viable way for roll control - aerodynamically that is. The mechanism you describe is a proper servo tab, where the aeroforces on the tab are fed back, and the tab acts like a lever on the main control surface. This was the way the post WW2 airliners were controlled, before they got too big and fast and only hydraulics could do it.

However, as usual, an aerodynamically beneficial solution has some serious structural drawbacks. An aerobatics plane can do 6g and the wings must be seriously strong and resistant to bending and warping. Normally, a wing has two spars which form a torsion box with the upper and lower skin.



If this torsion box can extend from wing tip to root, it is a strong and light construction. But if it has to be cut somewhere and the two wing halves are to be connected by a hinging rod, that spot will be a weak spot in the wing. It can be made strong enough, but the real problem is wing stiffness.