I'm think both him & Roy will be back only now they'll be 1 character, sorta like how 1 of Diddy's costumes is Dixie. In fact when he said he doesn't want any clone characters I'm thinking this is what he meant, I.E Doctor Mario will be a costume for Mario, Falco will be a costume for Fox (I think someone said he also has Wolf O'Donnell). The only question is will these clone characters play even slightly different as they did in Melee (Dixie HAS to have some differences).
FYI, costumes does not mean different models. All it means is the character's costume color looks like another characters. Mario has a color scheme that resembles fire mario. Fox's outfit looks like the same color as Wolf's. Diddy Kong's outfit is the same color as Dixie's (
http://www.youtube.com/watch?v=iO_MjeQipww). Peach has a Daisy color scheme. Different color schemes do not affect the way a character plays at all.
Roy making it back is unlikely since he was only added in as a promotional character, but Marth has a pretty good chance since he's the original FE lord.
As for Sonic's entrance, you can see it here (I hope...I'm at my school's campus and I can't see the video myself from this computer):
http://youtube.com/watch?v=Xevted1Xu-4