(names struck out are ones I feel aren't viable)
1. Banjo-Kazooie - Never played the games, so the two hold no sentimental value; they're pretty screwed from the business side as is anyway.
2. Isaac - Never played his games, but wouldn't mind him; he could be like Robin, primarily sword but mixing it up with magic stuff.
3. King K. Rool - Dropping cannonballs, blunderbuss spiked-cannon shots, crown tossing, helicopter pack flying, pro boxing, even turning invisible... you name it and K. Rool can do it! Would be ecstatic to see this krazy guy return. He has an amazing arsenal, and is one of the wackiest (yet oddly darkest) villains in Nintendo's library. What other villain steals their rival's food to starve them to death just because, or feeds his own minions to his pets?
4. Shovel Knight - An awesome character, but hasn't even appeared on a Nintendo console the Japanese side! They hold a pretty big sway on what shows up. It could be like another Sonic scenario, but I'm not holding my breath...
5. Solid Snake - Another great character, but with the current issues of Konami and Kojima, I wonder if it's even possible?
6. Bayonetta - ...If Tharja couldn't even make it as a trophy, Bayonetta's even worse off.
7. Paper Mario - Like K. Rool, tons of moveset potential, there's no way he'd be a clone since he's not restricted by time; can turn into a paper airplane, roll himself up like a newspaper, squash himself into a spring, and we might finally have a Mario that uses a hammer!
8. Wolf - With Lucas back, there's no way Wolf isn't. Totally fine with it.
9. Inkling - I REALLY don't like the idea of these things. But I can't deny them showing up; Roy showed up in Smash before his game was even released, the same could easily happen here. Probably wouldn't buy them, though.
10. Ice Climbers - The 3DS keeps the duo out..
11. Roy - Almost certainly a lock after finding his victory tune in the Mewtwo patch, and Sakurai's attendance of the FE 25th anniversary concert. Hoping for a moveset update like Falco and Ganondorf got for SSBB (clones alongside Roy in Melee).
Out of the oversaturated 3rd party reps people want to see, I'd argue Geno has one of the best chances. Hopefully something can be done with that complicated legal relationship between Square and Nintendo.