To me,

,

, and

are either going to become alt costumes or get the axe entirely.

I also think has a good probability of being cut, but not as much, because while he's completely his own character, he's sorta in this weird position I feel. Like, not only is he third-party, but he is currently the only SE rep, has little presence on Nintendo systems outside of Smash and cameos in FF spin-offs, and the way his series was represented in Smash 4 was kinda half-assed I feel. I also have the feeling that he's either going to be replaced with a different Final Fantasy character, or someone from a completely separate Square-Enix IP, but who knows really.
Next, I think that

isn't completely guaranteed, but considering that he came out when Mega Man was already in the game and he doesn't suffer as much from the kind of problems that Cloud has as mentioned above, I'd hardly rule him out.
Finally, while idk if

will be cut or not, if he/she comes back in Smash 5, he/she will probably be an unlockable character due to Wii Fit not being relevant in a long time, and the Trainer lacking the "WTF" factor now than when he/she was first revealed.
Pretty much every other veteran in Smash 4 I'm pretty confident is safe, albeit to somewhat varying extents.
In terms of veterans coming back, I think that

is highly likely due to being cut in Smash 4 only because of 3DS limitations and they are rather popular couple, so to speak.

is also probably coming back as well due to his popularity, but probably not as high of probability as the Ice Climbers.

and

probably aren't coming back due to newer Pokemon demanding more attention, and if Squirtle and/or Ivysaur make a comeback, I highly doubt it will be in their

form.

is an interesting case, while he's very popular and has a unique moveset, I think he's going to keep us waiting due to general licensing issues, Konami not being in a very good spot, and that he was cut from Smash 4, even though it came before the Kojima vs Konami debacle went public and TPP hype was building up at the time. Anyway,

I think is highly unlikely to come back, but I feel that there's a very small sliver of hope because Sakurai might do it to troll people. Finally,

was replaced by

, plain and simple; he has no chance.
So yeah, there's my take on all this.