I agree about Kid Icarus. It seems they're doing to Smash Bros what they did to Playstation All Stars (franchise-over-representation)
I'd go with Pac Man as well. If anything, it's Smash Bros or bust for a Pac Man rep. I can't see it in All Stars or any Xbox version that comes along. So Smash Bros is the perfect fit.
Shulk is the most likely as his game was a smash hit. Professor Layton as well. He was a main franchise for the DS. He will appear in some form whether it is a full character, assist or just a trophy. To not have Layton is an insult to the DS era. Same with Phoenix Wright.
A zelda rep is guaranteed due to the fact they included Rosalina and Greninja, both from Mario and Pokemon's most recent smash hits. So Skyward Sword is confirmed. Just a matter of who. Fi, Ghirahim, Impa and Demise are all possible. (Groose was a joke btw :P). I didn't think about ALBW missing the train so Yuga is out. Character wise anyway.
Though if we assumed that my theory is spot on (which in this sentence I hope it isn't), than that means there is only really 4 new character slots left. Someone deserving won't make the cut.