Cloud, Sephiroth, and KOS-MOS will never be in Smash 4 on the grounds that they never appeared in a game on a Nintendo console. And Cloud's appearance in Kingdom Hearts for the GBA and DS's KH: CoM and KH: Re:Coded doesn't count either. As for Shantae... I dunno who that is, sadly. Megaman has a good shot if Nintendo decides to bring in third party characters again.
Technically, Cloud has appeared on a Nintendo system. There's a 3DS rhythm Final Fantasy game coming out with him in it, so he has a shot, although it's almost zilch.
Also, KOS-MOS did appear in some Japanese-only Xenosaga games for the DS, so she's eligible. Also, Monolith is technically owned by Nintendo and makes games for them, increasing her chances. But that's not saying much.
Shantae is the protagonist of
Shantae for the Game Boy (a cult classic released at the end of the GB life) and
Shantae: Risky's Revenge for the DSiWare, but also has almost no chance of getting in.
Agree on Mega Man, he has the best shot of all third-parties.
y.toonlink said:
It's one of the reasons if Lucario gets replaced by Zoroark. I know that Mewtwo was planned in Brawl stuff, but it's also the same reason why I think Lucario replaced it (PT with Pichu).
Technically, Mewtwo was not replaced, just dropped.