As for Smash 4, there's no telling what the physics for that game will be like, so Meta Knight receiving a buff could be necessary, or for all we know, he may need a nerf. It all depends on how Smash 4 plays.
I wouldn't bother trying to base my buffs/nerfs on undisclosed game physics that leave me in the dark guessing. It's much easier to base it on the most recent build of the game (Brawl) when making comparisons.
From the remarks of players and spectators over the years, it seems like Brawl's gameplay mechanics/physics are just a little underwhelming, generally speaking. I don't necessarily share that opinion, but if we were to look at it from that perspective we can say that if Brawl in is entirety is 'slow' and 'floaty' and 'overly defensive' then we can conclude that also applies to Meta Knight as there is no exception made for him and he is part of Brawl.
Granted, Meta Knight is a faster, more aggressive character that is seen and played often in Brawl. With this in mind we can say that he is more like the gameplay that those players and spectators enjoy more, according to their stance. This would indicate to me that Meta Knight may possibly need buffs in this regard; buffs to speed that is to say, but still trying to achieve an overall balance with his relation to the other characters. (the Project: M videos were a good example of speed/combo buffs for Meta Knight that didn't result in an overly-powerful character)
Even if Smash 4 ended up being 'Brawl 2', I still see instances where Meta Knight could receive buffs. His Dimensional Cape, for instance, would need a stronger slash. His U-smash could also use a buff in some way to make it more useful. These buffs of course would be in addition to any necessary nerfs (specifically Mach Tornado) which would then result in an overall more balanced character.
This is why I said that I wouldn't mind seeing buffs for Meta Knight. Buffs are intrinsic to balancing MK as we know him, but people hear 'buffs' and 'Meta Knight' and jump to the conclusion that he automatically becomes Over-Powered.