In case this wasn't clear...
We know practically NOTHING about this move. We don't know how the power meter builds up (by hitting people and not getting hit, by charging, etc). We don't know the range or speed of the attack, and we don't know if he'll have any combos into it.
Heck, we don't even know if it WILL be a 1HKO (See the DK picture).
Speculating at this point if Mac will be banned is a ridiculous hobby.
Also, if it is true to the games, and he loses a chunk of power when he gets hit, then nobody will ever have a reason to complain about him.
"ugh that punch is so broken...."
"Well, you should have hit me..."
In related news, Mac is going to be a hilarious noob punisher...