I would argue that Dolurrh is very Shadowfell-like too. The fluff for the Shadowfell is that it's the place souls go upon death, to make their journey to where ever they're goin'. Very Dolurrh.If its in D&D, it has a potential place in Eberron. Everyone misinterprets that one.
Anyway, Eberron already has an exact duplicate of the Feywild (Thelanis). Heck, it actually has two flavors of Feywild (Lammania and Thelanis, even). Mabar is essentially the Shadowfell.