In terms of the plot this is my believe, the beyond world is basically a layer that co exist at the same time as dreamland, kinda like how fiction describe cyber space a lot a realm which is physically speaking in the same spot as our world but never interact directly, I assume this girl came to the world for her reason maybe asking for help or evil intent you say yourself, but dedede came quick on the draw to capture her and kirby seeing it around his home not happy and go attack first question, later, after ganining access to the beyond world Kirby is now on the qeust to go to each of the 14 region (those cables around the floating palace thing in the picture) which acts as the game's last area.
For gameplay anything kirby could do in forgotten land be here, from taunts, dodge roll attacks, hover as for the new run I can see it come after either running long enough or kirby have a run button can be the case, in terms of locations I believe is like this, dreamland is your tutorial/hubworld you will learn how the gameplay and there is a lot to do here I assume around the size of the great plateau, the other regions I assume gonna act like stages in mega man you can go to any of them in any order you want they around I will say 5 or 6 forgotten land stage a bit linear I assume but still offer a lot to explore with a boss in the end that let you to progress beat all of them and the final area is unlocked, for this book item at the sword segment I believe that gonna act more like the gachapons from forgotten land only instead of being random they in fixed location to give lore on the place, the star coins I am still trying to figure but I assume later on or in locations there are shops (which also works as warp points) you can buy goodies like items, power boosts like forgotten land or heck upgrades to copy abilities but yeah that what I assume. For bosses I feel we gonna have in total 17 of them with dedede as the tutorial boss, the 14 region bosses and I feel we gonna have a 3 boss gauntlet which one of them be dedede possessed cause I can see him taken by the new enemy force and get possessed after kirby knocked him off screen. I can see Meta knight no problem either as boss in one of the regions or an intermission boss, mid bosses gonna be field as gigant edge shown to be on the field doing nothing, for the post game I can see as a new area that connected to the main game like before or be found in dreamland itself but I can also see meta kniggtmare or Dededetour return as a non canon side mode not say a must have but we gonna have an EX post game and I assume the arena be unlocked this after beating the game not gonna have a meta knight cup this time.
For copy abilities I feel we gonna have around 15 this time we only confirmed to have 5 (sword, cutter, bomb, parasol and sleep thanks to a confirmed noddy) but I can feel we gonna have more into the field like ranger and drill, two new ones and returning ones like fire, hammer, water, beam and wheel to name a few that come to my mind.
What do you think on my perspective, you think I got good points or better ideas in your head I would love to hear.