Considering how Sakurai said that all DLC characters would be "of the unexpected kind", this seems unlikely… unless we play the "that's what they wanted you to think" game with that. But nah, chances are that all DLC characters will be like Joker: franchise-introducing characters nobody – or very few people – would expect.

(And no, the plant does not count as breaking this rule: that was a bonus character they added for the lulz)

If the next DLC character is revealed during E3, you can expect people coming here to comment "And I'm _____"