If it's Ninty's call I fail to see why a Nintendo-exclusive character who has been highly requested to the point he got a Mii costume is 100% out of the running like you say with Geno
Also you realize what you said with Banjo? "The trademark renewal is meant for the N64 Mini"...so they're working with Microsoft to bring back B&K which makes him...less likely?
This what I think:
Sakurai truely wanted Geno but couldn't get full rights in 4 so he made a Mii costume. Planned it for Ultimate, Square got stingy, so he dropped the idea as a whole. To not look bad (and since many won't understand), the calls were transfered to Nintendo... and Nintendo does pure business.
Geno's sole chance resides in if Square was specific that their IPs be DLC but then again, what negate that is that Sakurai said matters went to Nintendo's hands (not his), see. Yeah he got a costume, that was Sakurai's extent. And frankly, he's as exclusive as a receptionist signed cereal box. It may felt good one day but it's not worth much nowadays, which I think the way Nintendo looks at it (not Sakurai).
Yes, since again, we're talking pure business calls here (Nintendo). So let's go through some things in regard to each..
Banjo: Nintendo were the ones who kicked Rare staff out, the true Rare staff are now Playtonic NOT the Microsoft Rare, Nintendo was jelly of B&K games (Miyamoto), B&K had only 2 games on Nintendo. Really, Nintendo doesn't adore B&K at all, only fans think so.
Minecraft/Steve: Remember the Survive together ad.?, MC designed 3DS, a game with millions of players, a game still current, a game fresh in Japan.
So, which do you think business wise makes Nintendo drool the most? Smash being an advertisement game, it'll follow that suit, that ad, that "survive together" ad., it's definitely the most lucrative out of the two. Oh and Nintendo won't stop there, they'll use Banjo fans to sell their 64mini. An extra bonus from that MC deal. And that's the win-win situation.. business wise.
I'll tell you though, I truely hope I'm wrong, as I really really don't like Steve, and I think Geno fans waited long enough.