I personally just don't enjoy the combo character aspect, and having played as just Zelda for so long, would really enjoy seeing the two split up. That and it's not really something applicable to any of the more modern games.
I hope they declone Toon Link further. He has a lot of potential to be a unique figure, but so far it's kind of squandered unfortunately. Up-B with the Deku Leaf, Side-B Hammer, and I'm sure a bunch of other potential ideas exist. Heck, could do a Down-B Iron Boots for a big stomp like effect, if they really wanted to. The only one I think that doesn't really warrant changing is his Up-B, since the Spin is what I associate most with Link. But a lot of options, either way.
And I really don't think Ghirahim warrants inclusion. I'm fine with people wanting him, but he doesn't feel like a figure who should be in. But as I said with Skull Kid, even if he isn't really deserving of being in (as his only real noteworthy inclusion would be MM, second TP), I still want him. *shrugs* Hopefully that makes sense. Though, Ness comes from a series with... only a handful of recurring characters. I think the only series that has less recurring figures would be FE (at least in terms of ratio).