For December, I'd actually like to see some veterans mixed with newcomers, similar to the E3 presentation.
Wolf and Snake would be the best choices in this regard. One of them, both of them. You know the drill. Ivysaur and Squirtle aren't bad picks either, though I'd rather see characters from other series given Mewtwo is DLC already.
I think there should be a balance between newcomers and veterans in this kind of presentations, to which I add that it's always been the case for almost all special broadcasts.
Smash Bros. Direct on April 2014
Veterans: Yoshi, Sheik, Zero Suit Samus, Charizard - Newcomer: Greninja
Character reveal stream on July 2014
Veteran: Captain Falcon - Newcomers: Lucina, Robin
E3 2015 Smash Bros. DLC presentation
Veterans: Lucas, Roy - Newcomer: Ryu
The only exception would be the 50-Fact Extravaganza, but even so, it was when Bowser Jr.'s trailer was officially shown, along with Mewtwo's reveal. Again, veteran and newcomer combo.
Of course, this is just basing off a pattern and I'm not keen on doing such things as patterns can be broken anytime, but I'm kind of hopeful it goes like this once more.
I think Wolf and Snake have both their chance at the December presentation. Snake would cause hype and "complete" the third-party character line-up. Seriously, with Mega Man, Pac-Man, Ryu and Cloud having been added all at once in this installment, along with Sonic returning, it's begging to have Snake back.
Speaking of third parties, with Cloud being confirmed, this installment added double the amount of third party characters than Brawl, with 4 newcomers.
Wolf is more or less on the same level of popularity as Snake. The fact he's a pseudo-clone character that uses assets from other characters and is relatively easier to add could be an opportunity to appease fans. It also helps that he's got a new game coming next year.
If only one is to be added, I'd say it will all depend on whether Sakurai and Nintendo manage to secure a deal with Konami. Should it happen, it's natural that Snake gets more priority given the licensing costs.
All in all, here's hoping we get to see a few more faces from previous Smash games along with other surprises.
I'm getting that Wii U bundle with Xenoblade X.
I'm so getting that along with a copy of Smash Wii U.