Sorry I'm late to the party, and I'm sure this has been said many times already, but... If the 4chan leaker dude is right, as he seems to be with the mural characters, then Dixie was close to making it in, but was cut. And to me, that says she may have started as an echo but was scrapped for being maybe a little too unique and requiring more work than initially thought, not unlike Isabelle.
Also unfortunately, Dixie Kong is simply a lower priority character than Isabelle, both in terms of popularity and importance to Nintendo (and I say this as a huge Dixie fan and as someone who's never played New Leaf). So I could definitely see Dixie being cut, but then having more work put in to make her a semi-clone, and hopefully for DLC. I mean, so far so good in no sign of her showing up as anything else, but we'll see come next Direct.
Hoping for DLC. Dixie's Last Chance.