Different crossovers have different takes, but when looking at Smash as a context, they've essentially never deviated from a mascot or protagonist as the inaugural character for a new series. It's been that way for every series.
By the Smash fanbase's definition, Min Min is not a protagonist in the same sense as say, Spring Man. I think that's fair, nor would I disagree. But Sakurai specifically mentioned this in his presentation, so if it didn't play a role in how characters were chosen I would think he wouldn't mention it at all.
Like i said earlier though, being in the home stretch of such a large roster, and with candidates for new series largely consisting of lead protagonists or mascots, it seems that chances are things will continue to be "mascots" or "protagonists" for the inaugural series picks.
Candidates:
Pokemon Sw/Sh- based on what we know, could very well be tied to the anime (though from what I've seen there's no indication of the Pokemon that would stand out as of yet)
Xenoblade Chronicles 2- Probably Rex as he's the clear protagonist
Waluigi- not an inaugural pick
Bandanna Waddle Dee- not an inaugural pick
Golden Sun- Isaac is the clear choice. Protagonist
Astral Chain- Howard siblings. Protagonists
Ring Fit- Ring Fit Adventurer. Mascot/Protagonist
3rd parties are even clearer, so I won't bother posting them. But it seems to me that arguing, "See, there COULD be a non-protagonist pick" (even though Min Min doesn't entirely support that imo) seems to be merely looking at it with that point in mind, and not the implications for further picks. With a Volume 2 that seems to have at least 2 3rd parties who are much more likely to be protagonists/mascots, that leaves potentially 3 slots open for a new series or game to pick a non-mascot or protagonist.
It just seems like a rather safe bet at the junction that we're still going to get mostly mascots or protagonists going forward, and I don't see what the fuss is about with that at this point if i'm being honest. The only reason it would be a big deal at this point is just to shoot down a forum argument that, frankly, will probably continue to be supported in some capacity.