This and another post inspired me to say this:
The feywild of Athas isn't extinct, it's dead. You can go there, but it's empty. Like, if you've read the Twins series from Dragonlance, the Abyss in those novels. It's a gray, featureless plane, with a gray sky, and nothing in it. This is enough to have powers that interact with the feywild still work, such as various teleportations.
However, the other idea is that Druid groves have a bit of the real feywild in them. The better groves have a yellow sun if you get deep enough, and are cooler and wetter. You get REALLY deep in an epic level druid's grove, and the sun is freaking blue. Basically, the feywild is a windless, featureless plain of grey, still grit for ground, gray sky, with SUPER oasis's where powerful druid groves are. In fact, the motivation of druids could be to resurrect the feywild.
And the Grey I think might be the Ur-shadowfell.