Mart,
Look in Stepniewski and Keys where they explain how rotor stall works. The issue is that if you slow down the rotor enough, you raise the control loads (amount of stall) and thie requires beefier control components (servos to blade horn) or lower lives. Often, maneuver requirements occur in a split second, with no time to recover rpm.
A better way might be to have a high lift device on the blade, so that it reacts to the need quickly. The piezoelectric flaps come close.