All right, so after playing Planet Robobot, I've noticed SEVERAL details in the game that reference towards the current continuity of games- Namely, Sectonia being resurrected, the Dark Matter clone, Star Dream being a Clockwork Star, Galacta Knight's imprisonment, etc. And given all of the other little clues and info out there, I've been trying to piece together a timeline. This is mostly a theory of mine on the Kirby story. It's not perfect, and feedback is appreciated, so this is what I've put together so far! Suggestions and other evidence is welcome!
Okay, so let's just start at Kirby's Dreamland (KD) at the very beginning, since this is before Kirby has copy abilities, Dedede lacks most of his powers, and so forth. We at least have a beginning, but to add more to the timeline, I've decided to work backwards and look at Planet Robobot.
Based on information from Planet Robobot, Triple Deluxe takes place before, due to Sectonia's clone, not to mention the remnants of her flower being found. Likewise, Return to Dreamland happens before TD, due to the Sphere Doomers and prior knowledge. Thus, we have Kirby's Dreamland and the 3D Trilogy (RtD, TD, PR).
Based on a post by Shinya Kumazaki, it seems more than likely that Necrodeus was the one who made the Sun Stones to rob Floralia of its light, and presumably, prevent the Dreamstalk's growth. This would mean he'd have to have been alive around TD's prologue, so Mass Attack (MA) presumably takes place after TD, possibly even before PR.
Additionally, we know Amazing Mirror (AM) and Canvas Curse (CC) happen before TD, as Dark Meta Knight seeks revenge against Kirby and the gang in that game, as does Paintra, who seeks to avenger her fallen sister. That gives us KD, AM and CC (in no particular order), then the 3D trilogy, with MA happening after TD at the very least. And MA explicitly happened before Squeak Squad (SS), so it happened somewhere along the way as well.
Going on, we know that Kirby's Dreamland 2 (KD2) happens prior to Planet Robobot, due to the presence of the Dark Matter Blade's clone- we can also assume that the Dark Matter Trilogy happened relatively close to each other chronologically, so for now, let's just say that the DMT happened before the 3D Trilogy. Additionally, Rainbow Curse might take place after Return to Dreamland at the very least, as Bandana Dee is clearly friends with Kirby in that game.
So that then gives us KD, AM/CC, the Dark Matter Trilogy, the 3D Trilogy, and then MA and RC. SS is somewhere before MA. Furthermore, SS establishes that Revenge of Meta Knight (RMK) happened prior to it, hence the presence of the sunken Halberd. And we know Dyna Blade (DB) happens before RMK, since Dyna Blade acts as an ally to Kirby.
Kirby's Adventure (KA) seems to also happen shortly after KD, as Kirby and Dedede are stated to have recieved their newer abilities in that game. This would make KA the second in the timeline, fittingly. This now leaves Gourmet Race, Great Cave Offensive, Milky Way Wishes, and Revenge of the King left. There's also Epic Yarn, but I'll touch on that later. Now, if we assume that the games in SSU happen consecutively (with the exception of Revenge of the King, due to Dedede's blatant grudge), then this means, for the current timeline I've put together...
-Kirby's Dreamland
-Revenge of the King
-Kirby's Adventure
-Dark Matter Trilogy
-Canvas Curse/Amazing Mirror
-3D Trilogy
-Rainbow Curse
-Super Star Ultra
-Squeak Squad
-Mass Attack
-Epic Yarn
Now, I placed Revenge of the King right after KD, since it's meant to be a remake of KD's hard mode, just as Spring Breeze was a remake of KD, hence why Spring Breeze is not included as its own separate adventure; it's a remake, and so is Revenge of the King. As for Epic Yarn... if I'm honest, I kind of just tacked it on at the end. There wasn't anywhere that seemed to fit aside from after KD at the very least, and given its lack of contribution to the lore, I didn't worry about it too much.
And thus... this is the timeline I've put together. It's not perfect, and the placements of some games are interchangeable, but to avoid too much confusion, I've kept the trilogies consecutive, alongside SSU's sub-games. I might do a sort of story-serial type of post to explain the progression of the games later on. In the meantime, PLEASE, if you have ANYTHING to offer, comment! I want to keep this timeline as close as possible, and new evidence will always help. I'd also like to see anyone else's versions of the timelines as well, so we can compare our research!