I'd say Ness is pretty much definitely in, and Lucas is... eh I'm saying 50/50. I have my doubts about him returning for some reason.
Ness - 100%
Lucas - 75%
Either E3 or he's a hidden character I'd guess.
I think we'll get a last batch of both veterans and newcomer at E3 and the rest will be hidden characters. I'd wager Meta Knight, Ness, Falco, Ice Climbers, Ike and Snake if he's back will be at E3, as well as Mii, Pac-Man and maybe... Palutena?
Rest of vets will be secret, and a few more newcomers (Shulk, Chrom, and let's count Mewtwo as a newcomer?)
I feel great relief upon reading this. Thank you.