I'd wager a Kirby RPG being a Mish mash of elements from Paper Mario, Pokemon, and some of the Final Fantasies.
Kirby can adapt his class based on enemies he fights, eventually getting Milky Way Wishes style powers to let him keep it with him at all times. Power ups would be kind of Rock Paper Scissors like the elements of Pokémon are... Some types are particularly effective against certain enemies, and others are ineffective. Party Members work differently for each one... The helper characters have their own attributes and act a lot like Paper Mario partners in the overworld, and can "morph" with Kirby like in their games to give different attributes to Kirby's abilities. Meanwhile, Dedede Meta Knight and Bandana Dee would be your dedicated hammer sword and spear abilities respectively. Hell, add Gooey in to act as a secondary Kirby. I miss Gooey. So much.
There could be a "Limit break" kind of system with Ultra powers from Return to Dreamland, and use different Air Ride machines as sort of Chocobos and other vehicles to traverse the overworld, leading up to the final airship being the Halberd. Summons could be of Helper characters, I.E. powered up versions of regular enemies.
...I hate it when I think of awesome things that will never happen.