hahahahaha......hehehehehe.....ha. ha. ha.
Fake. This is just so fake. This simply won't happen.
ONE: Lucina, Dark Pit, and Doctor Mario aren't grouped with their franchise. It's been an unwritten rule with the devs for the past three games to keep those in the same series together in some way. The only possible aversion was with Yoshi in 64, but even then, he was only different in that his difference was vertical instead of horizontal. In Melee, Young Link and Ganondorf seem to avert this, but then again they are still one slot/square away from each other, the only difference is vertical. In Brawl, any differences were horizontal as well due to the vertical nature they took with aligning that time around. Also, stages from the same franchise are usually grouped together as well.
TWO: Duck Hunt Dog? really? You can't seriously say that Duck Hunt Dog could possibly be anything better than Bandana Dee. He doesn't even help you! He LAUGHS IN YOUR FACE when you miss a duck, not to mention that's one VERY old game that as far as I know, has only one entry in it's entire franchise. Not to mention he doesn't even have a name. His only role is to be a background element. A very annoying background element at that. Heck, Dark Pit, who I support even though doubting, seems on paper a WAY more likely candidate, especially considering Lucina and possibly Toon Link.
THREE: Who does Duck Hunt Dog even belong too? Certainly NOT Nintendo! The only game I've played with him in it was one that never releated to the NES or SNES in any way! I certainly never saw him on the N64. As much as I and many MANY others would LOVE to punch his face with Mario or my/theirself, he seems more suited to the role of Assist Trophy anyway. He's never been playable, or had much of a personality besides laughing at your legit mistakes because of the stupid game mechanic ducks flying out of your reach too fast. I know Sakurai worked with Little Mac, but then.... Little Mac is a character. He's a boxer an he's been in a fighting game. If Sakurai absolutely couldn't have come up with those moves Mac has, he could always use ones from the other boxers, such as the Egyptian's Teleport Spam move as a recovery. Can you really make any moves out of Duck Hunt Dog, or atleast enough to warrant a point in being playable? Maybe he'd be unique, but that'd only come from relying completely and entirely on ducks... Which even then, would be dang near impossible even with Sakurai's creative mind.
FOUR: I'm sure some people support Duck Hunt Dog, but I just have to ask, can you really, totally and surely, make a moveset for a character with nothing going for them? Pac-Man has moves because of multiple things. He has his old attacks, he has the spawn-random-stuff-and-people-relating-to-Namco ability people fear Toad would end up with, he has limbs to punch and kick with, among many other things. (This is one of the reasons I haven't exploded about Pac-Man since that post from long ago that will never be spoken of again: His moveset shockingly works, even if it IS what people use against Toad ALL THE FREAKIN' TIME.)
Even people who hate Bandana and think he's generic are still able to see that he can DO something, right? even if they think it's just him spawning random Kirby items to use, they could atleast make a moveset for him.
FIVE: There are Brawl characters missing that shouldn't be. Where are Wolf, Lucas, and the Ice Climbers? Wolf was only partially a clone, but his move stats and overall EVERYTHING were different enough that he didn't fell like a clone at all, unlike, say, Falco over there. Lucas was also more semi-clonish, essentially a type of "Luigi" to Ness. His specials all functioned in a slightly different manner, such as PK Freeze vs PK Flash, PK Fire leaving what's basically a campfire for multiple hits on a single foe vs a diagonal line to hit multiple foes with a single, decently strong attack. And of course, if Rosalina's far more complex style can work on 3DS, (as well as Olimar's,) then there's ZERO reason to exclude the Ice Climbers, especially in favor of Duck Hunt Dog or something.
Please note I refrained from the "Doctor Mario as a Costume" argument. As we've established with Lucina, if a character functions even slightly differently, they get a different slot, and Doctor Mario DEFINITELY functions the slightest bit differently from normal Plumber Mario.
Sheesh that was a long rant....