Feywild is both new and yet not; D&D has had faery-like planes kicking around for a long time (Elysium in particular comes to mind although a specific Feywild-like plane of faerie was an alternate in the 3rd edition Manual of the Planes. I doubt that's the first time it had appeared in D&D, although I admit I don't know off-hand of an earlier appearance), not to mention their provenance from actual folklore, that serve as prototypes for feywild. Shadowfell being radically different from (as opposed to a little bit of new development within) the plane of shadow is a hard sell too.The funny thing is, thanks to 5E the Great Wheel basically stole some of the best ideas from the World Axis (Feywild, Shadowfell, and even a version of the Elemental Chaos). Doesn't leave the World Axis with as much distinctiveness (in terms of structure - lore is a different matter).
That said, I think what 4th edition did with them specifically were among the more popular developments of that cosmology and they were seen as salvageable in a different cosmology, whereas much of the rest of 4es cosmology hasn't been mentioned since.