As much as these two would make for a great addition to the game, these two actually making the roster is highly unlikely. As much as it may sadden me to say so because the two of them would at least make my top five as far as dream roster goes for the next game, the reality of the situation is the company that owns them doesn't even qualify as a third party developer to Nintendo at all in fact they're quite the opposite. Rare Ware was bought by Microsoft from Nintendo to make them a second party developer to their console after the era of the Nintendo 64. They were re-branded as simply "Rare"and all of their content is now the intellectual property of Microsoft. Who are one of, if not the biggest competitor to Nintendo within the gaming market.
However this doesn't stop me from making a video talking about what a cool pairing they could be. Kazooie could be used for special A and B attacks. Where as the rest of the time you combat using Banjo's brute strength. On a more creative level, you could create different gadgets from the material in the jungle like they do in the actual games. It would be difficult to implement but still very interesting to say the least. For more of my opinion on this idea watch the video below.