I do think there are expectations that will be broken this time. For reference, I have nothing against ANY of the following characters/ideas, but I'm just saying what I'm thinking.
First of all, there are 30 Assist Trophies that we know of. The Direct stated that there are "over 50 Assist Trophies in the game". If it were more than 60, it would have said, "More than 60", so going off of that, I'm going to think we have 21-29 left to see. That's
plenty opportunity for a number of characters to be assigned that role. Shadow, Ashley, Isabelle, and several others could easily be assigned that role despite their popularity. During the Smash 4 days, Isaac from Golden Sun was a huge request, yet was actually
cut from the Assist Trophy list.
Sakurai mentioned the change he made to Wii Fit Trainer because of a request from the developers. I don't think it's out of the realm of possibility that the developers of Animal Crossing would maybe...NOT want their mascot, Isabelle, put in particular situations. Now, I'm not saying it's a reason she wouldn't be in necessarily, but I could see it happening. That comic strip earlier is funny, but I think there's food for thought there.
Here is the Assist Trophy video listing all of the confirmed Assist Trophies thus far:
https://www.youtube.com/watch?v=_XonAjPlq-8&feature=push-u-sub&attr_tag=iV0qwCEMDvbDeGgq-6
I expect great stuff from this game, and despite the way some may take my comments toward any particular character, I'm quite open minded to anything once I get a chance to play them. I simply DO think there's a tendency to double down on a character being in, and that doesn't always lead to the result we think.
After all, last time this site was absolutely sure K.Rool and Ridley were in the game. Now, the characters that are referenced are Isabelle, Ashley, and a few others. Popularity doesn't necessarily dictate the roster entirely.
Being an Assist Trophy doesn't mean you're absolutely playable material. It means you've been an Assist Trophy in Super Smash Bros. I believe the only two AT's or Pokeballs to become playable are Little Mac and Charizard. To me, that seems more like an exception than a rule.
In some cases, I'm hoping I'm proven wrong.