While I've never been a huge believer that Kamek would be a playable character in Smash, I would like to throw him some pity defenses cause I feel like the poor guy's picked on so much. In terms of his character, Kamek is about as iconic in the Yoshi games as Yoshi is, even if he doesn't appear in all of them Kamek appears very frequently when he does. As for the issue of being just a Magikoopa in Japan, allegedly he was always intended to be unique, if not by name, though I don't put much water in that defense since I can't really give a source for it. Additionally, Magikoopas are a unique enemy on their own, barely showing in most games outside of important events or stages, they're about as far from being a generic enemy as generic enemies get.
As for his moveset, Kamek would be a dedicated summoner. In addition to all the Yoshi enemies mentioned before (or whatever you categorize them as), Kamek commands his Toadies, who are pretty unique to him. Combined with his broomstick and enchantments / debuffs he could provide, and Kamek would be a real fun and unique character in Smash.
The problem is that Kamek's playstyle would probably be at least glancingly similar to Ashley, who is almost assuredly more popular than Kamek. But hey, I'll never say Kamek is likely, but I would enjoy his presence and I think he's the best option for a new Yoshi rep (since I'm not hot on Baby Mario for Smash).