The way I'm seeing it, the characters are becoming less of what you wouldn't expect, and more of ground-breaking fan-favorites.
In fact, all of them are ground-breaking, but they're essentially characters that are still highly requested by fans.
Joker came completely out of left-field, so it was hard to tell at first if the general scale of DLC would follow suit, being unexpected, yet popular and well-known characters.
I wouldn't exactly consider Banjo or even Dragon Quest to be completely out of left field, as Banjo-Kazooie and Erdrick (Hero) were already highly requested characters perhaps in the West and Japan respectively.
So, what does this mean for Bandana Boi?
Well, if I'm being pessimistic, it means absolutely nothing. Banjo and Hero aren't existing Spirits, and they're from franchises that haven't been represented in Smash yet, and since Ultimate is literally the Ultimate Fighting Game crossover, this might be the case for all of the characters in the pass.
If I'm being optimistic, this means that the characters might not be of the leftist-field picks anymore, which means that popular, fan-favorite characters are more feasible than one would originally think.
With that being said, I'm still mostly leaning towards all of the characters being from different franchises that haven't been represented in Smash yet.
(Hence the "Super Smash Bros. Ultimate X "Insert Franchise") trend that has been going on.
However, I feel that there could be a Second Pass. But, that pass would feature characters from existing or lesser-popular franchises in Smash or not. This means that at the bare minimum, we'd get new characters and nothing much else (unless a character's franchise is new to Smash), in exchange for less development time needed and the pass being sold at a lower price. If those characters are based purely on popularity, then I feel that Bandana Dee would be all but confirmed at that point.
So, yeah.
At this point, we'll just have to keep on waiting though.