Knuckles:
Chance: 1.3%
Within the realm of possibility. Sega and Nintendo have a good thing going at the moment, especially with Sonic exclusivity deal, and a fairly high chance that it will continue after the three game contract (Sega have mentioned that Sonic games sell far better of Nintendo, and it's cheaper to produce for Wii U so ya know, win win win). I also think Sakurai is enough of a fan of the classics to bring the original trio to rep sonic, Tails, Knuckle and Sonic; I honestly see Tails without Knuckles very unlikely (0.2%) and knuckles without tails completely impossible... others disagree with this, but that's how I see it.
I also don't think Eggman/Robotnik will be playable because his robots are so iconic (more so even than Wiley's, thus the yellow devil for Megaman), and would make fantastic bosses in adventure mode.. Shadow seems more fitting as an AT given his fan base splitting popularity, though he would get some chance as a last minute clone; more so than team sonic.
1.5% however is still very low, but not that low as third parties go. Lower than the likes of Bomberman or Simon Belmont even with the Konami Wii U debacle, but better than those Raymans and such. 1 slot per third party just seems right at this point especially with the Mario series' representation incomplete (Jr, Toad and Waluigi say hi), but I do see Sonic breaking this first, and maybe even quite soon.
IF SSB5 (or even a major expansion to SSB4) happens, and the sonic exclusivity continues beyond the three games, then I would vote team sonic's chances quite highly... up there alongside first parties, but right now there's just too many important first parties that have yet to be included.
Want: 40%
I honestly do want the Sonic Heroes trio, they would be great! (especially when they finally make a 6 player smash and you can have a team match of Mario, Luigi and Wario/Toad/Peach vs Sonic, Tails and Knuckles), but as I've said, there are necessary first parties sitting around untapped (elite four, Jr and Shulk as minimum) it would be insulting to put the Sonic characters before the many deserving Nintendo franchises. In Smash 5/4 Extend this opinion is liable to change assuming the roster's properly finished.
Lucina:
Chance: 7%
I previously considered her the more likely FE:Awakening rep, and this has changed, but not hugely. The big thing that's changed is my opinions on FE:Awakening getting a rep at all. I think that only hits around 20%. While awakening is hugely popular, the fact is that the game doesn't lend itself to a continuation series because it's set in Marth's continent, and uses Marth's sword. Sure they could continue with the way after Marth's death story, but it's less clear cut separation than Elibe or Tellius, and just to me doesn't lend itself as well to further conflict. Now, we do now know that both those series finished, but they didn't look like they had to, and Elibe had a second game, as would have Tellius if Brawl was released at the intended dates.
I don't see a continuation of the Ylisse and Valm story-lines (I'm sure partially because time travel means we've already seen the continuation, and partially because they're still basically Akaneia and Valentiam)... I'm thinking about 20% chance of the game getting a rep.
Want: 28%
With the same thought process I don't really want a one-off FE character, but I'd understand her inclusion, and I'd be somewhat happy she'd have been picked over Chrom, but not much. Ultimately however, if they reveal that Ylisse and Valm will get continuations then I'd pop that up to 80 odd % instantly.
Excitebiker: 1.4%
IF slime, an absolute legend, can't get over the body shape thing on this board, then I don't see how a wheeley popping biker who's stuck to his mode of transport, from a discontinued game, can.
Tails*5
Slime*5
(slime happy we're getting some goo-d characters to vote on, even if not the most plop-able)
*I'm out of practice on these puns
*