I don't know where things are going to fall in terms of Echo fighter vs costume. If we retain Alph as a costume for Olimar, then that begs the question of what makes for the qualification of an Echo over just the costume swaps. Is that decision just made on popularity? They continue to be in a weird place I think. It might also be an unpopular opinion, but I don't think we'll actually see too many echo fighters in the game. I feel like they were incorporated by Sakurai as a way to shut people up about clones and roster spots. Beyond that, he decided to make a couple for characters that could easily be a clone and he didn't see as much personal potential in.
Don't get me wrong, I love Daisy in as Peach's echo, but I don't want to see a ton of them either. Really the main one i support is Isabelle as an echo of Villager. Just changes her animations to more cutesy and expressive, and it's a way to get an Animal Crossing rep in without necessarily having to go through the process of making a whole new character.
I could see Jeanne for Bayonetta, Shadow for Sonic, and maybe Black Shadow for Captain Falcon in. Dark Samus feels a little odd when we finally got Ridley anyway, and anybody who actually really wants Dark Samus doesn't want that character as just an Echo I believe. Feels more like people just want to be right in predictions. Ninten is maybe an alt costume in my mind. I'm not sure Ninten has the fan base to justify full echo status, and Earthbound seems to already be getting a lot of attention in other areas. That might be slightly more supportive of him as an Echo, but I don't think the original Mother really has the cult status of the other two at this point (Could be wrong on that though). Chrom seems like one too many Awakening characters, Fire Emblem desperately needs more diversity in the character lineup too. A nod to fans is fine, and I'm not opposed, but his reasons for not being included in the last game make me doubt Sakurai would include him anyway.