Well, Dixie Kong (clone of Diddy Kong) and Mewtwo (Melee Veteran/semi clone of Lucario) could be comparable to Dr. Mario (Melee Veteren/more-than-semi clone of Mario) and Dark Pit (Clone of Pit).
Same thing with Chorus Men (WTF character) and Ridley (Brand New Villain) being foils for Duck Hunt Dog (WTF) and Bowser Junior (New Villain)
I don't know why people think Lucario is a Mewtwo clone. They only have
one shared attack. It's their neutral specials. If you think that they're clones, then you'd have to think that Little Mac is a Marth clone because they both have a counter as their Down Specials.
Now, to be on topic, I am still sceptical of this leak/idea, but it's rather intriguing. With Sakurai "thinking about" Mewtwo as a character, I feel that he was very aware of the desire. I mean, he's one of the Forbidden Seven (along with Dixie Kong and Doctor Mario). Plus, I do believe be was the most developed of the Forbidden Seven with sound files.
I think Dr. Mario started as an alt for Mario, but became its own character. They probably decided to make him a more competitive player by removing FLUDD and giving him his original Down Special.
Dixie Kong has already been considered to be a character before as she's one of the Forbidden Seven.
Chorus Kids have played a major role in leaks. With the Smash Run enemy from Rhythm Heaven (I can't remember its name), it makes me think a representative from the series will show up. I think the first occurrence of the Chorus Kids in a leek was the Gematsu Leak (which I think was debunked with the deconfirmation of Chrom as a playable character). But with the Smash Run enemy, I felt like there was a high chance for a Rhythm Heaven character.
Ridley has been desired since Melee. He's pretty controversial in the Smash Community. The status of Ridley in Smash 4 is currently unknown. It's known that Ridley is
in the game, but there has been no confirmation on his role (being a boss or a character or a stage hazard, etc.).
Now, I think having to connect the Wii U and 3DS to play as Mewtwo, Ridley, Chorus Kids, and/or Dixie Kong would be
extremely strategic. Being some of the most desired characters, it would be a great way to sell more Wii U systems.