Ness and Jiggs are definitely back in. They're long time veterans and they have no reason to be cut.
Falco was one of the few clones to survive the transition from Melee to Brawl, I think that speaks volumes. Not to mentioned he was changed to a semi-clone, but he is also very popular among the competitive community. Seeing as how Nintendo is catering a bit more to that side (For Glory Mode, GameCube controllers), it would make sense.
Ganondorf is the main Zelda villain. No way he's gone. Whether he gets a new moveset is yet to be seen.
Ice Climbers have already been mentioned by Sakurai. He said they were having trouble implementing them, but that was a while ago and they have had plenty of time to work out the kinks. Rosalina also pretty much debunks that theory. Besides, if the GameCube could handle four ICs on screen, I'm sure the 3DS can.
Mr. Game and Watch is staying as well. No reason to cut him. He was shown in the Pac-Man trailer as well as the Amiibo segment. He'll likely be a secret fighter.
Meta Knight is definitely coming back. His stage Halberd has already been shown, he's from Sakurai's own series Kirby, and he's very popular. Just expect him to be nerfed.
Wario will also be coming back. Ashely was already shown as an assist and Waluigi was even listed under the Wario series. No way he's getting cut.
That just leaves Lucas, Wolf, R.O.B, Squirtle, Ivysaur, and Snake. Those last three are likely getting the boot.
So that brings is to Lucas, Wolf, and R.O.B. I feel like these three could really go either. I feel like two out of these three will be back. ROB I feel has the strongest chance. That narrows it down to just Lucas and Wolf. Honestly, I feel one of them will be back and the other will be cut. Whenever that is remains to be seen.