I don't see Bandana Dee as REALLY unlikely, but I think that adding Bandana Dee before other characters like Ridley (of course), K. Rool, Shulk, etc. would be horrendously unfair to the series that need representation and don't have much of it in the form of PCs already (like DK/Metroid style). That's basically the premise of me not being too big a fan of characters Rosalina very much. The difference is that I sorta understand Rosalina because the Mario franchise is Nintendo's most well-known franchise. Adding another rep to Kirby that isn't really very well known a character compared to others would feel like an injustice to me because Kirby has three characters already. I think that it would be selfish of Sakurai to rep his own series further and not other series that need repping. Plus, if you give Kirby four reps, it puts it just under Zelda, Pokémon and Mario. Kirby is an important franchise to Nintendo, sure, but I wouldn't say it's popular enough to warrant that. I mean, Metroid is commonly viewed as a very important franchise to Nintendo (to the point where it often gets thrown in with the likes of Mario and Zelda) but its section would be perfect with Ridley. If Ridley were added, I think the Metroid section would be as perfect as it can get as Metroid as a series is right now.
Bandana Dee could be unique, but I'd be pretty annoyed if Bandana Dee got in over someone like K. Rool or Shulk.
Because of the other franchises that should really get more reps before Kirby does (since a lot of people argue that the Kirby section is perfect as it is now), I really have a hard time believing that anything outside of developer bias would get him in without those other characters getting in too. I think that he's not ridiculously unlikely, but his chances are overestimated a lot by people.
But hey, that's just what I think.