I feel like this is inevitably going to wrap around to Erdrick and his chances, and yes I do agree that iconicity (god I hope that's a real word) doesn't play as big of a factor as we think. We got Richter Belmont for crying out loud.
Buuuuuutttt... I think DLC is a different beast entirely. Yes, we got Corrin as DLC. But that's because of their interesting moveset that no other character could do. They sold us on Corrin because they had a cool moveset, the same way they sold us on Piranha Plant. Meanwhile, I look at Erdrick, a character who is more unknown outside of Japan than Corrin was before their DLC, and I think to myself "Why would they pick him?" The only argument is that he's the most popular protag in Dragon Quest, and only popular in Japan. I'm sure Western polls would be split between 11 and 8's protag. But popularity isn't everyting. Sakurai has commented that he factors in how unique a character is alongside popularity. Cloud got in not just because he is quite frankly one of the most popular JRPG protags of all time and known to audiences both east and west, but because the limit system was a unique way to translate the turn-based combat of Final Fantasy through a character who's game introduced the name "Limit Break."
What does Erdrick bring to the table that no other character can do? Be it his body type like Piranha Plant, or his gimmick like Joker being a 2-in-1 character with Arsene? Or Ryu and his Street Fighter inputs? How do you translate the simple, turn-based combat of Dragon Quest into Smash through a protag like him when Cloud already does a damn fine job at it?
This isn't even discussing the PR nightmare that would be trying to convince casual Smash fans outside of Japan to drop $6 on him if he really has nothing interesting going on and is unknown to the general audiences. It'd be like if Melee made you pay $10 to unlock Marth and Roy.
Then again I feel like this image kinda sums up what I think might happen come E3:
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