(Okay, this post turned out longer than I imagined at first, but I guess I got carried away. Without further ado...)
Lots of discussion around here, even though Chrom was disconfirmed. Impressive how you don't give up on the possibility of DLC, even though my pessimistic tendencies would be telling to not even bother trying. Anyway, I should start by wishing you all good luck.
So, I dropped in here to say some people have been misinterpreting Sakurai's words and calling him hypocrite or illogical, even though they're missing some crucial details.
We all know Fire Emblem: Awakening was a big thing last year (2012 in Japan). The main protagonists of the story are Chrom, Robin (the player's avatar) and Lucina. Of all those, Sakurai chose the latter two, even though Chrom is undeniably the main lord and protagonist, being the character the player has to bring along in every mission.
Sakurai explicitly told his reasons. Keyword here is "his", implying subjectivity. He's the game designer, the director of the game: the main creative force behind it. As a consequence of existing conflicting opinions among people, it's natural not everyone will agree with.
Of both Chrom and Robin, he chose the latter using similar arguments as people had been using, me included: Chrom was another swordsman, while Robin fit into the "Magic Knight" sort of character. Fitting the former, we already had Smash veterans Marth and Ike, both also from the Fire Emblem series. The latter had magic alongside swordplay.
At the first glance, which stands out more? That was Sakurai's question. Of Chrom and Robin, which would give that oomph regarding the roster's variety? Would it be another swordsman (with blue hair)? Or would it be a character focusing more on magic? Most people would agree on the latter.
From the perspective of many Fire Emblem players/fans, it almost would seem that there was something lacking regarding the series' characters. Both Marth and Ike are swordsmen (even though they have very distinct styles without a doubt). However, there is more to Fire Emblem than just swordsmen. There are archers and there are mages. Robin brings magic to the field and is the first Fire Emblem character in Smash that doesn't solely use a sword.
If you were to see it from the perspective of someone who never touched a Fire Emblem game before, they could get a wrong idea of what the series is about. How can other series offer many diverse characters, yet all that Fire Emblem has are swordsmen? With Robin, people who never played Fire Emblem will see there's more to Fire Emblem than just (blue-haired) swordsmen.
Sometimes it may not look like it and it surely varies between each individual, but first impressions are important. Robin has a more impacting first impression than Chrom does, especially after Marth and Ike had been revealed.
So far, all newcomers have something that makes them stand out from the remaining cast. That's the direction Sakurai is going, like it or not. You have the Villager from Animal Crossing who fights with random stuff, you have the unexpected Wii Fit Trainer who fights with Yoga poses while delivering lines you'd hear at a gym, you have Little Mac's boxing style, Rosalina's Luma and so on. Robin does bring something new, as I mentioned before: ability to use swords and magic. You won't find that on any other character in this game, will you?
Faced with such a philosophy, Chrom was doomed to not being playable, even if, without a doubt, he could bring something new to the gameplay. I'm not denying that and never did. However, it's like I said, first impressions are important. Newcomers here all brought a feeling of NEW to them. A feeling of freshness compared to other characters.
So... all this talk about first impressions, uniqueness, variety, oomph and impact... What about Lucina? Isn't she just a Marth clone? Indeed, she doesn't fit the same bill as other newcomers. She's probably the clone character that is the most similar to the character based from. It's really saying something when the differences between Mario and Dr. Mario or Link and Young Link in Melee are greater than the ones seen between Marth and Lucina in this new game.
However, Sakurai stated how she was "a lucky newcomer". In other words: she's an exception to what could be an otherwise universal rule or philosophy regarding newcomers as I've mentioned above. It all makes more sense when considering she was meant to be just an alternate costume for Marth down to applying changes to the model, voice and name displayed. The developers decided to make her something a little more than that by taking an existing character (Marth) and do minute changes.
Compared to the other newcomers, the resources spent on her were certainly much lower. There was less work necessary in designing her and no need to do any complications, since most of the work for her (modelling, texturing; not the animations since she uses the same as Marth's) has already been done so she would work as originally intended (Marth costume). I would even dare to say this could have even been done on the team's spare time or something similar.
Lucina only got in because the developers felt like it and because it was something very easy to do and likely wouldn't affect the game in the grand scheme. All of this to say that Lucina is on an entirely different boat as the other newcomers from a development point of view. Given the circumstances, anything that can be said about other newcomers can't be said for Lucina, and vice-versa. Lucina wasn't planned as her own character in the first place. Comparing her to the other newcomers is, for the lack of a better word, unfair or, perhaps, illogical.
This is all my opinionated analysis on why Chrom couldn't make the cut and why I think it will be a tough challenge for the Chrom fanbase to make him a DLC character. There are undoubtedly many creative ways to implement a moveset and fighting style to Chrom. He could have his own mechanics and have his share of unique and iconic moves, but what I explained above also counts a lot on what could affect a character's chance to earn a spot in the roster. More than some people might think.
All of this said, good luck on achieving your goal. You will need it!
PS - In regards to Robin's Final Smash in which Chrom teams up with him/her to attack the foe. We call all agree we could have another Toon Link-Alfonzo situation in which Chrom would be replaced by another character if he was in battle as well. Another swordsman like Lon'qu could use the same animations as Chrom for the attack. This would, of course, be included on the Chrom DLC.
TL;DR - I know it's long, but it really would be best if you took your time to read it.