I personally feel that Lucario, Mewtwo and Charizard will make return for sure due to the new Mega-Evolution and popularity, but I feel they're going to replace jigglypuff and possibly add a couple new Pokemons.
My first suggestion would be..... *cough*..
Second suggestion: Pangoro
This fella quickly became a fan favorite for alot of Pokemon fans when he was first introduce I believe back in Spring. Base on his design, I can definitely see a clear move set for Pangoro. From using the anicent martial art of kung fu to make a couple of dark type moves. The possiblies are endless.
Third Suggestion: Blaziken aka (Mega-Blaziken)
Same reason with Pangoro
What are your suggestion what new pokemon do you suggest should be in the new Smash Bros.?
“Don’t follow the hype, follow the games”
Here a little quote I want for those to keep memorize in your head for this coming next gen.