This is a weird theory, but perhaps it might be plausible. It was said that the roster was made-up early in development. While the roster is finalized, what if the characters weren't? The ESRB and other staff would know the roster so they can give appropriate ratings, but can't play as them. Potentially, they would get the ability to see their trophies, models, and the digital posters of the characters. So, ESRB, PEGI, etc. can still look at character Z and say, "Oh, looks fine to us. No suggestive themes, partial nudity, etc."
Someone also said that Shulk looked a little sloppy during fights - I never played Xenoblade Chronicles, but I seen some gameplay and I think Shulk wouldn't be a sloppy swordsman. Perhaps he's unfinished, but is developed enough they can show him off to the testers and raters. Kind of like how Link's stance changed from Brawl to the new SSB4 one and how Marth is getting tweaked since the recent demos were E3 builds.
What if Wolf and the Ice Climbers are in an unfinished state and can't be shown off now to the testers, but can be in the future?
Generally, most games when shown to testers, reviewers, and raters would be very close to finished or finished, but with some polishing left to do. Super Smash Bros., however, is a fighting game like all other competitive games need to be balanced and polished enough that little can break them. As an ongoing process of Q&A, bug finding, and tweaking, it might be possible that the build leaked is unfinished. Also, knowing Sakurai, he'd probably do as much as possible to make it perfect even if he gets hurt. Maybe a 90% complete build or even 75% one if it's really that bad and was the cause for the release date change.