In my opinion, there is a good chance that we will be getting another third party as DLC.
Sure, we did get Ryu, but he was developed before the Smash Ballot was a thing and on top of that, the Ballot says you can vote for your favorite video game character.
Plus, back when people thought you could only vote for Nintendo characters, there was that spokesperson for Nintendo that cleared up the confusion by saying they will be considering third party characters.
I mean, why put down "video game characters" instead of "Nintendo characters" if there won't be any as DLC besides Ryu? It's a safe bet to think one more will be coming.
As for who it will be, I'm going to go out on a limb by saying that Snake won't be coming back.
I don't hate the character. If anything, I would be really sad if Snake got cut, as that would mean none of the awesome Metal Gear music would make the transition.
I guess it's the art style that is Snake's biggest obstacle to getting in. Even in Brawl, I still felt as though Snake was a little too out place, but that's what made him unique.
However, he might be a little too realistic and dark for Smash 4's bright style. Combine that with Nintendo's shaky at best relationship with Konami, and Snake ends up being the odd one out for Brawl veteran DLC.
I could be completely wrong in the end, but I still think we're only getting one more third party newcomer. Who could it be?
My gut's going with Rayman, but I would love it if they bundled them in a DLC third party package that also contains Shadow Moses Island and the Glade of Dreams.