People have to stop overrating how different Chrom is, all we saw different with him was a balanced blade like Lucina, taking his up-b from another clone-compatible character (that most people also thought he was going to be Echo'd from to begin with), and possibly u-tilt being from another clone-compatible character (we don't know yet if Roy took Marcina's u-tilt back or not). We have no idea how Chrom and Roy compare in most facets, Chrom could very well have the exact same movement/physics specs and frame data, and have all his other moves being the exact same to Roy's except for a balanced blade, which would make him less different from Roy than Dr. Mario is from Mario. At best you can call Chrom an Echo with some slight hybridization, not a "semi-Echo" as I've seen some people claiming.
I think Dixie's chances of being a real newcomer are slim, but I think she is very likely as an Echo; even when overshadowed by K. Rool she still had a respectable support base and was certainly a much more popular demand than any of the Echoes we currently have, while being a prominent character in her own right who even got a relevancy boost, plus she was planned for some playable capacity back in Brawl. If she doesn't make it in the base roster, I think it could be because she was intentionally held off to be given the full newcomer treatment in DLC.
Don't mix up a character being considered as being "wanted" or "planned"; Ayumi was never "wanted" and was just a mere consideration that Sakurai passed over, and Takamaru wasn't even really considered in Melee (Sakurai was just responding to someone asking about Takamaru and dismissed it in a snide manner) while Takamaru was just another briefly considered character for Smash 4 that was quickly passed over. People thinking these two were ever "wanted" or "planned" really needs to reread
Source Gaming's Definitive Unused Fighters article.
Geno is the only currently unplayable character we know of where Sakurai outright said he wanted to make the character playable in a past game.