I wonder how would be the demiplane of Dearthdark (Dragonlance: Wild Elves) if a planar gate was opened toward the Athasian Tablelands(Dark Sun).
What planes from the cosmology of Magic: the Gathering could be added to D&D? For example if Ravnica is a megacity, other planets in the wildspace could be focused to the farming.
I miss new elements. I bought Manual of the Planes and Planar Handbook in the 3rd Age. Then I don't want to spend my money to read again the same lore. And this can be read freely in the fandom wikis.
Zagyg could create a new demiplane, style Ravenloft of Witchlight, but focused into comedic parodies style Castle Greyhawk.
Zendikar is roughly analogous to Eberron as an Adventure World, only if it was in adrift in Limbo / Elemental Chaos.
Old Phyrexia & Mirrodin / New Phyrexia is an interesting "Future World" plane, a sort of Shadowfell meets Mechanus
Ixalan is The Lost World + Mayaincatec Sun Empire riding feathered Dinosaurs + Hollow World + Vampire Conquistadores + Amazonian Merfolk
New Capenna is 1920 Metropolis + 1950s Gangs of New York (ft. the Five Families ruled by Demons)
Thunder Junction is Weird Wild West World
Kaladesh is kinda like Eberron but more Hindu inspired motifs.
Amonkhet is sort of like Dark Sun only a bit more Egyptian inspired.
Kamigawa is kinda like Kara-Tur, only now it's now half InuYasha & half Ghost in the Shell, making it a lot more interesting.
Innistrad is Ravenloft; Lorwyn/Shadowmoor is Feywild/Shadowfell merged into one plane; Eldraine is the Feywild; Kaldheim is Ysgard; Rabiah is Zhakara. These probably can be skipped or used as reference material for those other planes / locations.
There's a few other notable Planes and of course the 3 that have D&D sourcebooks – Ravnica, Theros, and Strixhaven (Plane of Arcavios, home to Strixhaven Academy). Ravnica is the most popular plane, hence why it got adapted first, recently it's become the Sherlock Holmes / CLUE type world too. It does overlap a lot with Sigil, though. Theros was adapted because of a desire for Greek Mythology world without being Greek Mythology. Kaldheim is kinda similar but feels a bit more Outer Planes than Theros does, which feels self-contained. Strixhaven is Magic School tropes.