I can't give very many concrete thoughts on Lucario as I have very little (basically none) experience playing against him. So I'll abstain from the rating and just ramble on about a couple of things I've been thinking.
@
Nysyr
is over-exaggerating Dedede's weaknesses in this match-up. Dedede has a fair number of moves just as fast as dsmash and that are (relatively speaking) safe when the Dedede spaces properly and respects his opponent's options. Nair, jab, Bair, retreating ftilts, I think will be seen a lot in this match.
From the small amount of time I've spent with Lucario in the lab, I find he's in a similar boat as Dedede in that many of his attacks have a lot of recovery frames, yet Lucario lacks a lot of the range Dedede has thanks to that hammer. I also think Lucario's movement speed is kind of mediocre. I might be completely wrong here, but it feels like Lucario is going to try to zone Dedede out with aerials, Aura Sphere, Force Palm, and weave his way in up close where I'm sure Lucario has the advantage.
On Extreme Speed: Dedede's main goal isn't necessarily going to be chasing Lucario off stage, just to watch as he flies away and recovers from its end lag as Dedede floats back onto stage. Dedede wants to pressure you into going where Dedede wants you to go. Ideally, we would make going for the ledge unsafe and force you to land on stage some how... Perhaps by lodging a gordo on the ledge? If Dedede maintains stage control and forces you to land on stage, that's a stock you just lost - Lucario's recovery on Extreme Speed is ridiculous, no matter how slow Dedede's attacks may seem. I also fail to see how we can't simply whack you out of it with a well place fair/bair, anyways.
The main issue I see coming into this match-up is that for all of Dedede's power, he can have a heck of a time killing. And my limited experience against Lucario tells me that this character just doesn't want to die. And once he has aura and rage...the match-up becomes super obnoxious.
I don't really know what to think. There's nothing that sticks out to me that forces this match-up into being a negative one for Dedede (which is a pleasant surprise). At the same time, if Lucario gets to rage, and I feel like he probably will, it's easily in his favor.
On a personal note, the very very few Lucario I've come across online usually just tried to lame me out...but it was FG and most of those Lucario players were pretty bad. And some of the stuff they were doing definitely were assisted by the lag, as I recall.