I think that Magus420's idea is so that while everyone benefits with the auto-L-Cancel (more so for characters with laggy but powerful aerials, mainly the heavies, than those with little lag in their aerials already (aka Meta Knight...lol) ), those that decide to use Magus420's version of the S-Cancel will do so with some thought on the risk/reward in their minds.
With S-Canceling as it is, the risk/reward ratio is heavily in favor of reward without risk and it tends to shift the favor to the heavies and those with laggy aerials (Ike, Snake, Ganondorf, Link, etc), meaning the lighties with little laggy aerials, who gain only little to no (ha ha...Meta Knight again) benefit could potentially get shafted (well, perhaps not so for Meta Knight, though I say this again in jest) and fall behind very much.
With Magus-Canceling/M-Canceling (as Wind Owl named it), we will have some measure of risk/reward with Magus420's version of S-canceling such that heavies or those with laggy aerials will not mindlessly spam the S-cancel function, and put to thought whether or not they want to sacrifice their shield (the risk) in favor of a greater offense (the reward). At least, that is how I see it...and though it does make me somewhat amused to see Ike be able to swing his sword like crazy in the air all day without much fear or Ganondorf skull crush (fair) his opponents all day or Snake do a wall of manliness (aka bairs) or Link dair his way through his opponents, the S-Canceling as it stands tends to reward these with little risk (if any risk) at all. M-Canceling, I believe for the moment, might be the way to go...
Ha ha, Wind Owl...now you got me using that terminology. M-Canceling...heh heh heh...Chrono Trigger...