I think Kirby and the Forgotten Land will be the perfect game to reintroduce Rick, Kine, and Coo as gimmicks. They haven't fulfilled their use as ways to traverse platform challenges since Kirby's Dreamland 3. It would be cool to see how they would play in a 3D environment and I think they would work well into the whole nature and animal motifs. Here is how I envisioned them as playable:
Rick-I think Rick would be used extensively in more open areas where combat is emphasized. He would work well as a buddy that excels in clearing combat challenges. I also think his rock copy ability would work well with slopes in platforming.
Kine-Definitely would be used in water levels. He could be used to swim through water much quicker on the surface or underwater. Assuming this new Kirby game reuses the elemental mechanics in Star Allies (I hope it does) I envisioned Kine's electric light bulb attack to cause electricity on the surface of the water to clear enemies.
Coo-I initially thought the new game was open world, instead it seems to play like SM3DW. I thought Coo would be a cool way to traverse the open world, but that idea fell through. It also wouldn't work on individual levels because there is a height limit. So instead, I think levels that can only be completed with Coo would be best, (i.e. where there is no solid ground to stand on). I imagine these Coo-centric levels would play like the Robobot Jet sections in KPR, but with a z-axis.
Don't worry HAL, these ideas are free. But seriously, I really want these 3 to appear in the game, almost as much as I want DDD, MK, and Bandana Waddle Dee to appear. Idk how Pitch, Nago, or ChuChu would work because they are all kind of reskins of the other 3 animal buddies.