I'm very excited for this new installment to the series! I love the other three games, and how Brawl was able to get third-party characters. Sonic and Snake were great choices, but could be argued as overpowered and hard to control sometimes. They were great to play as and I hope they are still included. If not, hopefully the new characters make up for it.
I like how this is going to between both the 3DS and the WiiU.
As for the characters they've mentioned, Villager was an odd choice, but I can't help but be excited to play this psychopathic citizen. You should see the internet memes of him, they're all over the place.
I still have not played the Megaman games, but for some reason I buzzed with excitement when Megaman was introduced. He's one of the most requested characters from fans to be in a Smash Bros. game, and they finally got him in! I'm so happy for that.
As for the Wii Fit Trainer, when I first found out, I was like; "....... what?" I told my friends after school and they too were like; "....... what?" But one thing's for sure is that the series needs more female characters since the only ones are Peach, Zelda, Samus, the female Ice Climber (but technically you're controlling the male character), and if you consider Jigglypuff as a female pokémon.
In terms of other characters I can think of, I hope they have Ghirahim from Skyward Sword. As for more female characters, the only one I can think of would be Dixie Kong. I know some people would say Rosalina, but I don't think it's necessary to have her as a playable character. In terms of third-party games, they got Megaman, so that's one big wish come true for fans. The only other character I could think of would be Rayman, due to Rayman Legends because it used to be a WiiU exclusive. I'm so excited for that game, and the gameplay alone, you can see him as a Smash Bros. character easily. There's not much I can think of, but I totally facepalm to those stupid fans that request characters that were never associated with Nintendo, like Nathan Drake or movie characters that have nothing to do with video games. I know some fans may think this would be awesome, but it would be so stupid if they had Wreck-It Ralph as a character. There are fans who request this kind of crap, not realizing it's a Nintendo game. But in the end, let's hope we get a good roster.