Not gonna pretend I know anything about the background or how graphic arts work, but things can change. There can be inconsistencies; there are inconsistencies in artwork all the time.
And at the same time, it's just a promotional picture. It is not a definitive confirmation or deconfirmation. If anything, the text leak a month back by ChadG anondorf is the big "proof."
Also most of these characters are gonna be in anyways. Isaac and Chorus Kids felt inevitable as DLC at least, Shadow and Ken felt like easy choices, Geno and Banjo make a ton of sense and got a lot of demand (especially the latter), and Mach Rider is one of the best "forgotten retro character" candidates that has been thrown around as a concept before in Melee.
In addition, this fits Chad Ganondorf's leak.
Again we are going to get most of these characters. We are getting DLC and other characters. If your favorite with a good shot isn't here, don't panic. You can wait for DLC, and the roster is already too good as is. Game's roster as is right now is the best roster in any game I have ever seen for anything ever. If that's not enough to satisfy roster nerds, IDK what is.