I noticed a topic on gamefaqs that brings up an excellent point that Sakurai himself stated that utterly demolishes the concept of Steve being playable and gives Banjo and Kazooie much more of a concrete argument for inclusion.
http://www.sourcegaming.info/2015/07/11/gdc-2008-translation/
Lets start with this, an interview where Sakurai details why some characters are chosen to be fighters.
To quote Sakurai,
Standard for Selecting Characters:
・The character must display personality in their game
・It’s important to have something only that character can do.
・Potential development issues, and game balance is also taken into some consideration
・ Distribution among the franchises is also taken into consideration
Point 1 is already a Steve-killer, since the Blockhead can't emote or show ANY personality or physical movement aside from "move limbs". His limbs are not articulate and all he can do is wiggle his arm to imitate swinging a tool. Going back to Banjo & Kazooie, we all know that they both show immense personality in their games. One great example is their Idle animation where Kazooie pops out to bonk Banjo's head for a laugh. In action, they both show personality with how one uses the other to function as a whole character.
Point 2 can apply to our Duo as well considering no other character has their unique charm and aesthetic aside maybe Duck-hunt. Even then the Duck-hunt similarity just boils down to "Mammal with Bird" and I trust Sakurai isn't going to toss Banjo away just because of that.
Take good notice of the 3th page under the section of "Parameters" This really puts Steve at a huge disadvantage because in order to work as a fighter, Sakurai himself states "Characters are created as a combination of their source material and Smash's game design and dynamic characters." Banjo and Kazooie have tons of different moves, abilities, and animations that can be used as a viable moveset and just generally fit with the high energy of Smash Bro's gameplay.
I know im preaching to the choir here but this provides great insight into how our beloved duo should and WILL fit in as a Smash bros fighter if they do make it in.
I'm sure there are tons of other examples that demolishes Bricks-for-brains chances, but these stuck out for me.