I am genuinely surprised there were no vets revealed during E3, but I am less surprised now that I know the game has been delayed until October.
I figure, with a little over three months until release, and if nothing more is revealed in June, we could see one vet per month to finish out the starting roster, and that may be all we'll see before release.
Wario, Ice Climbers, Meta Knight seem most likely as starters. I've long felt that Meta Knight makes more sense as a hidden character, though the same could be said for any of the three.
Ness, Captain Falcon, Mr. Game & Watch, and R.O.B. seem more likely (to me) to remain hidden, for the sake of tradition (which may also apply to Luigi), but I wouldn't be surprised if any of them were starters.
Ganondorf and any StarFox character other than Fox I'm inclined to expect to be hidden.
Jigglypuff and Mewtwo, especially the latter, seem better suited as hidden fighters. I expect at least one hidden Pokemon character.
Lucas would probably be a starter again.
I'd like to see Lucas and Wolf return, because I hate seeing people's favorites get cut, and because they are important characters in their respective series, but I also fear that, after Squirtle, Ivysaur, and Snake, they are the most likely cuts.
I would expect any additional Fire Emblem rep, if we get one, to be a hidden character, as well.
We start getting into dicier territory from here on out, but I could see them saving one or two more newcomers to be revealed prior to release, and then keeping the rest hidden. Given that characters have been revealed at such a steady pace so far, with the occasional flood of info during special events, I'm going to go ahead and predict a starting line up of around 35 characters, assuming that, based on the precedent Brawl set, all third-party characters are announced prior to release and yet still need to be unlocked. I don't think 15 hidden fighters is too unreasonable.
At this point, I could see it playing out like this, and this is sort of just idle speculation late at night so forgive me if I missed something...
Starters:
1. Mario
2. Peach
3. Bowser
4. Rosalina
5. Yoshi
6. Wario
7. Donkey Kong
8. Diddy Kong
9. Samus
10. ZS Samus
11. Link
12. Toon Link
13. Zelda
14. Sheik
15. Kirby
16. Dedede
17. Meta Knight
18. Fox
19. Pikachu
20. Charizard
21. Lucario
22. Greninja
23. Marth
24. Ike
25. Ice Climbers
26. Pit
27. Palutena
28. Olimar
29. Villager
30. Wii Fit Trainer
31. Little Mac
32. Mii Fighters
34. Expected Newcomer
35. Expected Newcomer
Hopefully:
36. Lucas
Hidden:
1. Luigi
2. Ness
3. Captain Falcon
4. Mr. Game & Watch
5. R.O.B.
6. Ganondorf
7. Falco
8. Mega Man
9. Sonic
10. Pac-Man
11. Expected Newcomer (Chrom / Third Fire Emblem Character?)
Hopefully:
12. Mewtwo
13. Jigglypuff
14. Wolf
15. Unexpected Newcomer? (Snake? What happened? Snake? SNAKE! SNAAAAAAAAAAAAAAKE!)
16. Unexpected Newcomer (Ridley?)
17. Unexpected Newcomer (Isaac!!!)
18. Unexpected Newcomer (???)
So, about 50 total, give or take possible additions or cuts. 48 at minimum, but hopefully more. NOA's Treehouse during their live play sessions this week made a few comments in regard to the roster being huge and there being several more characters they're super excited for but can't talk about yet.
As for the slots I only labelled as Newcomer, you can pretend they are whoever you think.
For the sake of discussion, let's go with the Gematsu characters, as they seem to only be gaining popularity in terms of predictions.
If he's in, Shulk seems more likely to me as a starter, as does Takamaru or any other surprise retro rep, and if we do get a Rhythm Heaven rep, as predicted, I could see them saving that as a post release surprise. Or we could go with the theory that Sal's tipster only leaked the characters who would be revealed pre-release, so we'll say that the last space on the starting roster could go to RH Glee Club / Chorus Men, instead.
After release, I'd say we could still see up to four newcomers, including the aforementioned third FE rep. I'm not counting on it, but here's hoping. I'd wager at least two of the hidden characters will be new.
If we do get Ridley, after all the teasing and heartbreak, I could see him being one of the biggest secrets as well as being the most difficult to unlock. He just makes more sense to me as being a big secret.
I'm going to keep holding out hope for Isaac as a hidden fighter, even though I don't by any means expect him, because I am stubborn like that, and because we still haven't seen him. Isaac is, as far as I am concerned, the second most likely Brawl AT character, after Little Mac, to be promoted, because, like Mac, he had been featured in a new game in his series not too long before development of SSB4 began, and, unlike many of the other Brawl AT characters, he has enormous potential. Heck, I feel like he has a better shot than Ridley, oftentimes.
There are still many other possibilities, of course. We may not get another surprise Retro at all. Snake could defy expectations and sneak back into the game (it would be kind of hilarious if he was literally discovered hiding in a box somewhere in the game). We might still see a Zelda newcomer (here's hoping for Tetra because I want to be a pirate). Finally, I would still love to see the Donkey Kong series get a third rep. Between Dixie and K. Rool, I'd be more inclined to expect Dixie, just based on intuition. I'd gladly take either.
I'm going to adopt a strategy of not expecting anything more than 50 characters max, no more surprises, more cuts, and nothing else that I've been hoping for. That way if I see anything I haven't been expecting, I can be wildly excited.