Banjo collection or a new game would be released for both Xbox One and Nintendo Switch. Microsoft owns the IP, or at least the studio that owns the IP. They would obviously release it on their own system, as that makes sense.
The collaboration with Nintendo is what would bring it to Nintendo platforms, just like Cuphead and other titles.
Considering prior Smash presentations at E3 have had two reveals, I can see Erdrick and Banjo happening. Dragon Quest XI has an upcoming release and can be boosted in the West by a Smash pick, while the relationship with Microsoft gets stronger with Banjo coming back for Nintendo fans, a major demographic with interest in the series.
Banjo Kazooie is a big deal, mainly to the west and not Japan. Both reveals are major for different reasons, so to act as if one would completely eclipse the other is a tad of a stretch in my opinion.
If Erdrick is release immediately while Banjo release later this summer, there’s still a focus on both character independent of each other.
I think it’s going to come down to a Banjo-Kazooie collection at the Microsoft conference.