I concede, I cannot deny footage that is clearly running off the 3DS game and being shown on screen. No way that could faked.
As for how I feel about this roster:
Very happy with Bowser Jr. Not only does he look like a fun addition and they implemented him in a quirky way, but now less people can be angry at Rosalina's inclusion. I'm really happy for Bowser Jr's. most dedicated fans, and since I've always had a soft spot for the little tike (they may have squandered his potential as an engaging character after Sunshine, but at least he's cute), I'm personally happy he's here. Him and Rosalina complete the Mario roster IMO. No more Mario characters are necessary for Smash, we have all of the most popular and most important Mario characters. And it's an awesome set of characters.
Shulk seems fine, though I don't know anything about him from his source game, so I can't comment on much. Seems like a fun character with great range, and again, happy that people may get their #MonadoMonday soon!
Have nothing to get from Duck Hunt/Mr.Peepers, but in terms of WHO he is, I'm sure a lot of people will like him. I hope he plays great.
The majority of Brawl vets being back makes me very happy.
And I still don't like Dr. Mario. Found him the worst addition in Melee, and find him worse here, since we KNOW he can be done as an alt costume. I basically feel the same about Dark Pit and Lucina, but at least they are characters with their own fans so it's not QUITE as bad. I hope Dark Pit is better differentiated from Pit than Lucina is from Marth and Dr. Mario is from Mario.
Now, I know the roster leak is real...but what's the deal on the rest? I haven't caught up yet...
For my pre-emptive opinions, assuming the other parts are real:
The 3DS stage list will be disappointing to me. Too many Brawl/Melee stages and not enough new stages to off put that.
The DLC roster is great, and makes me excited to see Snake again.