Following one of my other posts here about DLC involving veterans, I have done some research on why these veterans won't return but this doesn't necessarily exclude their chances.
Pichu: This one is obvious, a weaker clone of Pikachu isn't needed
Young Link: No need for him since we already have Toon Link, a better character than Young Link
Roy: 5 Fire Emblem characters may be too much for a small series plus Lucina is already a clone of Marth so Roy may not be needed even though he had fire effects from his sword.
Lucas: I'm very sorry Lucas fans but Lucas will most likely not come back because Ness's customizable special attacks does include Lucas's attacks like PK Freeze and the variations of PK Thunder, PK Fire, and PSI Magnet. Check out Ness's [SSB 3DS/Wii U] page for more info.
Wolf: Wolf unlike the others, does have the highest chance I believe but Fox's alternate colors of gray fur and purple clothing highly resembles Wolf. This alt color didn't exist in past games and this alt color is most likely a way to compensate for Wolf's absence. Plus, notice how all the Star Fox character trophies all have their last names excluding Fox and Falco since their last names aren't used but Wolf's last name (O'Donnell) is on his trophy.
Snake: His inclusion is all up to Kojima and Sakurai agreeing to add him which may not be likely.
Ice Climbers: I don't know how to explain them since its technical issues and not Sakurai wanting to cut them for no reason. Hope is they get in the Wii U and the New 3DS versions while working around the original 3DS.
Squirtle & Ivysaur: Ivysaur was a personal favorite but these will more than likely not return. 7 Pokemon would be too much even for a Pokemon fan like myself. Plus, too much Generation I representation and Gen III hasn't gotten any yet.
So thats that guys, what do you guys think? Sorry to burst anyone's bubble but hey who knows? I may be completely wrong.