You know what I'd like to see?
Richard Halliwell's Lustria written up as a campaign background.
Originally springing forth from a jokey play upon the title of Erich von Daniken's Chariots of the Gods - which became Chariots of the Frogs in GW injoke speak - Lustria was a weird mix of ancient astronauts, once-advanced-but-now-degenerate amphibian beings, punk Amazons and, for no apparent good reason, Norse settlers and adventurers.
(I say was, Lustria still is, but it goes without saying that I'm talking about the days of Warhammer 2 and 3 and WFRP and not modern Warhammer)
It goes like this.
Once upon a time, the ancient Slann arrive on an obscure blue/green planet and shift it's orbit closer to it's parent star in order to alter it's climate, and then genetically engineer a bunch of helper/servant races. Once part of a great cosmic Empire, the World has two great warpy-teleport gates at it's poles through which interstellar traffic passes.
Then as a result of an unstated galactic catastrophe it all goes tits up and raw Chaos-stuff splatters through the warpgates, spiritually, morally and physically polluting the globe. Reality breaks up and goes all Moorcock at the poles, the Slann civilization collapses and everything goes a bit post-apocalypse.
Wind the clock onto the current year of the Warhammer World and it's South America analogue is a sprawling mass of Meso-American ruined cities once inhabited by the amphibian scientist race of the Slann that is now a primitive tribal race dying out at the hands of human settlers.
The human settlers are at war with the Slann and also with the remnants of their servant race, the Amazons, all of whom look like Toyah Wilcox in her prime, reproduce asexually via chemical means and have access to a bunch of Old Slann technological weapons such as, errmmm, bolt guns and bolt pistols. Also lobotomised and castrated human slaves with shaved heads.
So, lots of dungeon bashing in Chichen Itza, except that all the decor depicts humanoid batrichan super-scientists not Meso-Americans with bad haircuts. Unfathomable ancient technology, fallen civilization, ancient astronauts, jungles, disease, Norse homesteads, Toyah Wilcox and Christ knows what hiding in places where no White Man has ever been and underneath it all, the radioactive fallout of the dreaded Warpstone.
If only GW had chosen to write this up in campaign background setting back in the WFRP days.
As it happens, I'm not sure that WFRP would really be the best ruleset for Lustria. WFRP is so wedded to a low-fantasy, Germanic, urban game (the old "you start in an alley full of shit between two half-timbered buildings with double-headed eagles on their shutters" thing) that I don't think it would suit this pulpy, post-apoc goodness. It would really call for a White Box D&D treatment.