I see the extra content going one of three ways.
A) Exclusive to Banjo Kazooie
B) Exclusive to Rare
C) Microsoft in general
The latter would be ideal since there's a lot to work with. Any KI costume for Mii Brawler would be an instant buy.
I see A as most likely for music, B for Spirits, and C for Mii costumes
Reasoning:
The stage itself is from Banjo so all the music has to be from the series unless they pull a
![Pac-Man :ultpacman: :ultpacman:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
.
Since there exists data of Blast Corps/Jet Force Gemini spirit categories in the code, adding spirits could happen though since the data is unused and tied to the cartridge, this may not happen.
And of course, I need Mii costumes of Master Chief and maybe a Creeper Hoodie or Steve costume.
But remember, we're dealing with entirely unknown territory now since we only have one released DLC and they only came with Persona music, Persona 5 spirits, and Persona Mii costumes (plus the return of the Sonic costumes from 4). So who knows...