Okay, there's one important thing that just came to my mind.
I don't care what you say, but Sakurai, or whoever helps him design the character - they DEFINITELY had Banjo & Kazooie in mind when they made Duck Hunt. I think there's a BIG possibility that's the case.
And if it IS the case, they want B&K in Smash. They'd approve. Microsoft approves. Some one, like Iwata might not, though. But I think we'll have a quite big chance of getting him in Smash.
And I've been thinking for a while, that it would be kinda awkward to have both characters in Smash.. but now that I think about it again, Duck Hunt might even be a tribute to B&K, because in my opinion, it was greatly inspired by them, so Duck Hunt is simply a B&K inspired character with his own spin on it, and I think that's just ok.
Also, a lot of people say, that Microsoft would gain in this, and Nintendo would lose, but B&K in Smash could even be a deciding factor for a Microsoft fan to buy a Wii U and Smash.
Just think about it. There would definitely more cases of "Hey, look, it's Banjo in Smash, he really fits in, I want to buy a Wii U and the game now!" instead of "Hey, look, it's Banjo in Smash, now I want the upcoming Banjo game and an XBOX, even though I'm looking at Wii U and Smash right now!"