One important question that I did not see the answer for is: Does the reduced damage and knockback also mean the hitstun on the move is reduced? If the hitstun isn't reduced, then I can think of good ways of prorating your attacks on purpose.
Also, a lot of you people are thinking that this new mechanic is going to force people to use every single move in the arsenal, but why aren't any of you pondering the possibility of the opposite happening. What if it would actually be beneficial to spam the same weak attacks over and over again to build damage and increase the comboability? For example, lets take Marth, why not just spam f-air over and over, and since each attack is prorated, then it would lengthen the time you could keep someone in a combo as long as the hit stun stays the same for the attack. Then after you build enough damage, just use a finisher.
I know as soon as I get brawl, I'm going to be testing this theory out, finding some spamable weaker aerials and tilts to build combos and damage, then chain into finishing moves.