Don't know who you mean by "folks," but I don't know enough about Magic to be sitting on it. Sounds intriguing.
DRAGONS
The plane used to have massive 'dragon tempests,' where dragons were magically born out of thunder and lightning. The first five dragons each claimed territory as their own, and dragons born in those areas would become part of that elder dragon's brood.
Atarka was a massive and hungry bully, with smoldering antlers and fiery breath. Her brood hunted in the frigid steppes and glaciers, but would protect humans who hunted for them.
Dromoka was patient and merciful, her scales thick and her breath a searing beam of light. Her brood tried to teach humans of the deserts their morals.
Ojutai was meditative and cunning, lithe and feathered, able to breathe freezing gales. Atop remote mountain peaks, his brood gained enlightenment and learned esoteric magic, which they offered to those humans, in exchange for those humans erasing their own historical texts.
Silumgar was cruel and murderous, resembling a tusked serpent with venomous breath. In coastal jungles, his brood gathered mighty golden treasures and used necromancy to cow their humanoid minions.
Kolaghan was feral and free-spirited, covered in spines and wreathed in lightning. Her brood do not speak, but they will fight alongside the humans of the rolling plains in bloody raids on the other dragon broods, rewarding those who refuse to settle in cities or adopt any laws.
CLANS
There were also five main humanoid cultures, each organized around opposing one of the elder dragons.
The
Temur Frontier seem Siberian-inspired, with tight family bonds, warriors with ferocious strength, and magic-users called whisperers who sense visions of another world in the northern lights. They call that world the Unwritten.
The
Abzan Houses are Persia-inspired, building great walled cities, taming mighty siege animals, and focused above all on patiently enduring. When they die, Abzan willingly bond their spirits to a kin-tree, and can be called upon in times of war.
The
Jeskai Way is a clan of mystics and monks who value strategy over strength, with a distinct Tibetan vibe. They have a loose alliance of mountain monastery strongholds, each of which perfects their own fighting styles and magical techniques. They were committed to gathering knowledge and guarding written history.
The
Sultai Brood are Khmer- and Thai-inspired, a rich nation formed of an alliance of humans, naga, rakshasa, with expansionist goals but also a strong tie to their ancestors, the spirits of whom seem to live in the river jungles and lush farmlands.
Finally, the
Mardu Horde are Turkish- and Mongol-inspired, but without a strong central leader. Each individual warchief would seek to bring glory to their riders by hunting dragons, which they saw as vermin. Other clans would both scorn the Mardu and rely on them, since one year they'd raid them, and the next they'd slay dragons who posed a far greater threat.
THE CRUX OF FATE
There might always have been two versions of Tarkir, or perhaps the Unwritten became the Written. But the great spirit dragon whose presence conjured the dragon tempests was slain by a Temur shaman, who used magic given her by a being from another world to steal the will of some newly-birthed dragons. In that world, the tempests ceased, and the clans gradually cut down the dragon broods, until eventually only their bones remained.
In another world, however, the spirit dragon was sealed in a chrysalis of angular stone. When he finally recovered from his wounds, he emerged to find centuries had passed, and his five children had subjugated the humanoid races.
Who gave the Temur shaman the power to slay the spirit dragon? And who spared him? How did both realities come to pass? While Temur whisperers can see the unwritten, is it possible to step between the two worlds? Do the khans of the five clans have an obligation to save their kin and invade that other world, to slay the dragon tyrants once again?
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GAME MECHANIC OPTIONS
You want a 'Council of Wyrms' style option where players are dragons? You could do that in this setting.
You want a campaign focused on slaying dragons? Maybe create some new dragons with special abilities and weaknesses, to get a sort of vibe like the Monster Hunter video game franchise?
One mechanic from the card game was 'morph,' where certain cards had an ability to be played as face-down creatures, then later turned face up by paying a cost that varied card by card. While face-down, they were all identical - represented by a shimmering comet-like orb of gold or white flame. But you could turn them face-up to surprise your opponent, revealing some special power.
Narratively, this was tied to energy from the other timeline cloaking your real identity.
I'm not sure what you do with that as a PC, but it creates some cool adventure prospects, where the PCs can explore two parallel realities.
And since the whole setting is tuned toward facing big giant monsters, it gives them an opportunity to build new material for high-level play. Maybe go for a Dynasty Warriors inspired system where you can lead an army in mass combat (but with the same elegant speed of normal 5E mechanics, treating each army as just a big monster with stats and a couple special abilities)?
