You've seen those hybrid-like sets like the Bazooka "irons" right? I don't know that the Rules of Golf really determine this. I think a set of "irons" with "bulge and roll" would be allowed. So I don't think it's an RoG thing.
But think about the other reasons why you probably don't want your 7-iron to have varying loft and be pointing in different directions.
Irons still exhibit gear effect. If you toe a 4-iron, the spin axis is still tilted toward the draw side… and the ball still starts to the right, but neither as much as if you toe a 3W by the same amount. Partly due to the lesser deformation/ball speed, partly due to the lack of bulge/roll, partly due to the different placement of the CG (the iron head twists more easily, thus resisting the ball from making it twist less).