The original 12 from SSB64 aren't going anywhere, as per usual
No duh. :P
Ike will be replaced by Chrom from FE: Awakening
Why can't they co-exist? Sakurai has already expressed his hate on cutting characters. Roy was originally meant to co-exist with Ike in Brawl, but he, along with Mewtwo, was cut due to Sonic's late entry.
Mewtwo will return as playable, complete with his new form, possibly replacing Lucario
Again, like Ike and Roy, Mewtwo and Lucario were originally going to co-exist in Brawl (have you ever lurked into Smashboards?). The only characters who aren't safe by default are the third-parties.
Pokemon Trainer may not return either, instead being replaced by another Pokemon from Gen 6
The Pokemon Trainer we have now is way too iconic to be replaced, and Mewtwo's return will already represent Gen 6 because of its new forme.
Snake won't return, but Sonic has a high chance of returning, especially with his exclusives and Lost World on the way. He's practically a Nintendo character right now. xD
But there's a thing about guest characters in fighting games making only one appearance and never come back in the next installment.
Dixie will be playable to promote DKC: Tropical Freeze.
While she was originally meant to appear in Brawl as part of a tag team with Diddy Kong, King K. Rool has higher priority due to the many fan requests.
R.O.B. probably won't return (even though I liked using him)
Mr. Game & Watch wasn't removed in Brawl, so what makes you think R.O.B. will be removed?
Shulk from Xenoblade will be playable
He has a lot of requests from fans at Japan, so his chances are high.
Toon Link may return due to Wind Waker HD, but if not, he'll be replaced by Ghirahim from Skyward Sword
No, that will be Classic Link from ALttP, Link's Awakening, OoA/OoS, and ALBW.
Ghirahim will be playable regardless (this is pretty much my only wish with this game :P )
Except he's a one-time Zelda character, who aren't allowed to be playable. What makes you think Midna and Zant weren't playable back in Brawl? He's better off as an assist trophy.
Demise will make an appearance somewhere if Ghirahim is in, most likely an Assist Trophy if those come back
See my response on Ghirahim.
Reggie will be playable (please Sakurai?? xD )
Reggie himself said in a interview that will all be based on Sakurai's decision, so he asks Reggie to add him in Smash, then his body is ready.