Nearly all toneholes are uneven today - the lack of flatness across the rim has been a consistent problem down the years.Nearly all tone holes were uneven in the 20's and early 30's?!?!?! That's why Conn had Res-O-Pad, Buescher had "Snap-On " Martin "Neverleaks, Buescher and Conn didn't use shellack. A self leveling system? The pads were more to compensate for uneven toneholes. Another pad system on a Kohlert model 1927 straight soprano. No shellack. A very thick pad with screw and washer.
Plain drawn holes typically rise where the holes goes over the apex of the tube - probably as a result of the downward pressure from the milling (flattening) operation being relieved after the event.
With rolled holes you get what you get after the rolling operation, and later levelling is very time-consuming.
A self-levelling pad would really only work if the tonehole was perfectly flat - a flap valve, effectively. The slightest warp in the tonehole means the pad would be required to deform in order to take up the warp...and that would require increased downward pressure on the key cup and extra time for the pad to adjust. It's by no means a new idea, and can be seen on early flutes and clarinets which used a pewter 'plug' loosely suspended on a key, which dropped down into a tapered hole in the body. It didn't work very well.