Seeing this, and I'm just sitting here thinking "they're called 'Echoes'"…

Shadow: Honestly a big possibility, probably the biggest. He is the most popular character in the Sonic franchise after Sonic, he already has a model in-game and since we already have 2 Sega characters with Sonic and Bayonetta, wouldn't be out of the realm of possibility of another one

Ken: Another possibility since they only need to add fire effects to Ryu's moves, and Capcom has 2 reps already so they could add one more.

The rest? Eh, I don't know. Ms Pacman by all accounts is the same as normal Pacman, Dark Link doesn't have anything unique to separate from normal Link, Louie is just the same as the rest of the Pikmin characters and…….Zack? Of all characters from Final Fantasy, why ANYONE would want Zack?