Boy, it feels really weird posting a rating higher than the Chrom fans today, especially since I'm apathetic towards him at best, but here we are.
Chrom
Chance - 25%
I'm going to discuss a bit more than usual today, but let me put my basic argument up front: Lucina has roughly a 50% chance of returning as a non-essential clone (I'll get more into that once her day rolls around), and I believe if Lucina returns, there is roughly a 50% chance that Chrom will be an alternate costume for her. There may be some other plausible edge cases, but realistically speaking I think that's the only way this happens.
From my point of view, Chrom's chances are tied almost directly to Lucina's. He's already been passed over as an individual character, and I don't see any reason to believe that will change. It's not unfair to say that the most likely scenario is that Chrom simply remains a part of Robin's Final Smash (let's say that's a 75% chance since I don't expect Robin to be cut). We also already know that Sakurai thinks Chrom doesn't offer enough unique moveset potential to be worth including. I'm not going to argue for or against that point, but it is what it is.
What we do have is a playable Lucina, who is, at least currently, a Marth clone. What's curious about this is that Chrom and Lucina are relatively interchangeable in terms of abilities: Chrom taught Lucina swordfighting, and she even uses the exact same sword. This even translates to other games: in Heroes the abilities of their base forms mirror each other, and in Warriors they use the exact same moveset save for differing cinematic specials. If Chrom is too boring for Smash, theoretically Lucina is too boring for Smash, and yet she is playable. Maybe it was a simple matter of popularity, or adding another playable female, or Nintendo/IS wanting to promote Fire Emblem that much more, but one way or another she got in.
So the next question is what is different for Smash for Switch? In my view, it's Nintendo/Sakurai's evolving views on costumes in Smash. Ignoring how well Mii costumes may or may not have done, Sm4sh gave us Cloud and Bayonetta, who each have two costumes representing two iterations of their respective characters, Robin and Corrin, who got male and female variants, and Bowser Jr., a character whose 7 alternates are seven different characters. Clearly, Sakurai is not opposed to the idea of costumes being used to show pretty drastic variants of characters, and if Chrom and Lucina fight the same way, then we have a very viable way of getting playable Chrom.
No, Chrom was not available as a Lucina alternate in Sm4sh. Yes, Chrom was used for Robin's Final Smash. While I don't believe there is precedent of the former occurring, we at least know Sakurai is aware of Chrom's fans given that Final Smash and the original reveal trailer, so it doesn't seem unreasonable to believe he ends up back on the table for consideration. As for the latter, that is no issue whatsoever: seven Brawl veterans got new Final Smashes in Sm4sh (eight if you count Charizard), so not only do I not think it would be surprising to see more Final Smashes change, I think it would be surprising if there were no changes.
So that loops back around to my operating theory: if we're going to get playable Chrom, it will be as a Lucina alternate. Without going into specifics, I believe there's roughly a 50% chance of Lucina, and if that comes to pass, I think there's a solid 50% chance of Chrom becoming one of her alternates, which comes out to a 25% chance for playable Chrom overall. This includes the surprise case of Lucina being decloned (that makes a Chrom alternate that much more likely IMO), and in a sense also the case of unique Chrom (because why wouldn't that also affect Lucina?). I still don't expect it to happen, but I think it's very plausible, and certainly more likely than some of the other characters we've already considered.
Want - 50%
Like I said, I don't particularly care about him. So long as he doesn't replace Lucina somehow, sure, let him Smash.
Nominations - Lucina x5
I'll probably end up re-using some of the above on her day, but there's definitely some unique factors to consider both as a specific character and as a Smash veteran.
Rhythm Heaven Prediction - 43% Chance, 43% Want
ARMS Prediction - 77% Chance, 67% Want
The former benefits thanks to the idea of Chorus Men in particular, while the latter is one of the most obvious considerations for Smash Switch. I'm expecting two relatively strong showings, although I think want on the former might suffer.
EDIT: Bonus prediction: I don't think we'll get a Fire Emblem newcomer in the base game. Seems too late to get anything from FE Switch since we still know basically nothing about it, and even counting the popularity of Lyn in particular, I think Sakurai will be cautious regarding adding another FE character without good cause.