can you elaborate why you're conviced they'll join? just curious.
They have the best things going for them. Though in some ways it feels more like a process of elimination.
For instance I think K. Rool, despite being more popular than any of those, is being passed over because of Dixie Kong. Understandably, Nintendo would be reluctant to introduce 2 Donkey Kong characters at once, so despite being very popular K. Rool misses out (Inversely, if K. Rool defied my expectations and got in, it'd stop Dixie Kong from being playable).
Similarly I feel the same thing happens to Krystal, because Wolf is so likely to join, Nintendo will avoid having two StarFox DLC characters.
Inkling would be a fine choice, but the game can't even render the ice climbers because of handheld limitations, I feel that to implement them (and do them justice) would be beyond what's currently possible and they'll be left to Smash 5.
Bandana Dee simply didn't have the support when the ballot started. Look back over the early poll results that floated around back then and he simply didn't rank very high. That period, when the ballot was fresh and in the media spotlight, would be when most of the votes were cast. I think Nintendo decided very early on who they would pick, they're not looking at these last minute votes and seriously considering changing their minds.
It's on record that Snake got into Brawl as a favor to Kojima from his friend Sakurai. Now Kojima is gone from Konami, and the company's current direction seems to be going away from video games. He's a veteran so I wouldn't count him out completely but he seems very unlikely in my eyes.
So, when you critically look at the top choices for DLC, in the end you're left with only a few realistic choices. Rayman has by virtue of being popular enough, checking all the right boxes, and not stepping on anyone's toes become a great contended for Smash. Same for Issac, he's not the most popular choice, but he's in a good position strategically.