While Ice Climbers have a bit more history under their belt, no one thought Mewtwo would be cut from Brawl, yet here we are. Sure it disappointed some fans, but Brawl still sold 12 million copies. IC would probably have a few more disappointed fans, but I see no reason to believe the disappointment would be that much greater then Mewtwo.
In short people no doubt argued, "I just don't think Sakurai would put in clones like Toon Link and Falco over an original character like Mewtwo. It would disappoint fans," but it happened. That said the Doc is way more cloney then those examples, but I think that comes from the clone backlash that caused Brawl to have no true clones. I think Sakurai has since learned that people don't really know what they want. Sure they complain when they see a clone, but only because for some reason they seem to think the alternative is some fully fleshed out character instead of no one at all.
He hasn't said so, but I bet that same psychological phenomena is why he isn't sure about doing DLC (or at least last we heard officially he was). No doubt the moment they make any people will cry unfair, despite the alternative being a world were those characters, game modes, stages, or costumes simply don't exist.
That said, this leak could still easily be fake, and we get Ice Climbers! Just prepare yourself. Picture leaks near release have a far greater probability of being real. Since this isn't a zero probability and smash has a tendency to disappoint diehard fans with the roster (whether this is an issue with our expectations or with Sakurai is a topic I dont want to touch, but the disappointment itself is irrefutable), we should prepare ourselves.