Well now I feel a bit silly logging in, as I figured someone would mention him by now, but I'd really love to see Magolor. I know he's really only appeared in two games (and that's counting the 20th anniversary as a separate game, though it does give perhaps some indication on his future), but I think he'd be a nice playable rep if Kirby were to get one. My top five Kirby reps actually are...
1. Magolor, as I kind of said above, would be easily the top of my list. I love magic users, and I think Magolor would have a very unique and viable moveset. Obviously his odds aren't particularly good, since Bandana Dee makes more sense to include over him, and Kirby having five reps would be a bit much, even if I'd be happy. Still, I'll always support him most out of a potential Kirby rep.
2. Bandana Dee comes in at second. I really, really like Bandana Dee too. A spear user? Totally on board for that. And his inclusion would mean FE's weapon triangle is completed by Kirby first, which kind of amuses me (and if you include Magolor that's all of the major weapon groups pretty much, as Arrow is hard to pull off, though the 3rd on my list could count). His moveset is versatile and unique, would stand out from the rest of the cast, would represent a hopefully to be recurring figure in the series beyond the core three, etc.
3. Ribbon is the next on my list. I know, she's minor, a one-shot, etc. But I think she'd have a really fun moveset if playable, which is really part of why I want her. Plus a floaty ranged specialist (which is the impression I get from her) makes her really nice. I would love to see the Dreamland series represented a bit more, so seeing her in would be good as well. Though the fourth on the list could help with that too.
4. Dark Matter goes here. Not 0 or 02, but Dark Matter, namely in his swordsman form. I realize the possibility of redundancy, but I think Dark Matter could be an interesting and unique fighter, and Kirby's only recurring villain (at least consistent villain, DDD and MK switch too much to count). Final Smash being 0 or a bigger Dark Matter mass or some such seem good as well.
5. Here's where I can't decide. Honestly, I guess giving it to Knuckle Joe is somewhat fair, since he would at least clear Kirby's moveset of Fighter Kirby hopefully, and let him use different Copy abilities. But... really, barring the anime, KJ doesn't have anything unique on him. Closest he has is being the "main" helper in the Helper to Hero thing, and his Assist Trophy. But there aren't too many figures I could see. Galacta Knight, Marx, and Adeleine seem like the remaining contenders for the fifth spot, but I can't really rank any of them significantly higher than the other. I prefer Magolor to Marx, even if Marx came first and Magolor uses him as inspiration somewhat, Galacta Knight is cool but too similar to Meta Knight, and Adeleine as well as Ribbon might be a bit silly. Oh, Gooey could work, I could support him in the fifth slot. A bit of a one-shot, but reps Dreamland and Dark Matter, as well as being able to have a unique moveset.