Well, with MC we'd still have auto L-canceling, cutting ALR in half, or more. MC would further that lag cut by giving you zero lag, but you'll have to time the shield input as if you were executing a manual L-cancel. The known risk involved with MCing, and it’s a choice, is that it eats away a certain % of your shield each time you perform said technique. Is it possible that this would lead to shield breaking? Sure, if the MC is used foolishly, and spammed, you'll likely be punished in the form of shield breaking. However, the benefit of MCing is that you can follow up immediately, completely laglessly.
Your shield is in no danger of breaking whatsoever if you don't make use of MCing. Conversely, if you use MCing sparigly, and efficiently your shield should also be safe. The only chance you have at getting your shield broken is abusing MCing, poor spacing, and playing in too predictable a fashion.
The overlying point here is that MCing will add a wealth of depth to the game. It's not an obscure mechanic because you aren't forced to use it if you don't want to. Using it would be beneficial, sure, but it’d still be an option, not a necessity. One thing is almost certain; it would make heavies and strong characters frightening, giving them in particular a new bag of deadly tricks.
Would MCing create a campy game? No, absolutely not. There’s a simple reason for this. MCing is NOT just a mindless button press, but a tactical option. You’re never FORCED to MC against your will, as such; you’ll never jeopardize your shield unless you willingly do so. If MC wasn’t an option, if it was downright mandatory, then your shield would always be in a vulnerable, or in a near vulnerable state, as such, then it would create a campy game. Only if MCing mandatory would gameplay become campy. The game would literally play out just as it does now, if you don’t use MCing, and there will be virtually no effect on shields.
In the end, I really think MCing would be very beneficial to the game. It’s something that every character can utilize, some making better use of it than others. It’d add some technical skill the game, requiring intellect and skill, for abusing MC is quite costly. I strongly think that MCing is just the mechanic we could use to create more depth in Brawl+.
It’s such a great idea! I'd love to see this in the next build (I mean to say the one we wait 5 or so months for).