I wouldn't mind a return to homelands set, the plane hasn't been revisited and it had some interesting lore than could be expanded on.
Ulgrotha, whose name means "Garden", was a small backwater plane, far from Dominaria, sometimes called the "Homelands" by its inhabitants. Its mana lines were destroyed ages ago when Ravi rang the Apocalypse Chime, causing the Great Destruction and ending the Great War between the Tolgath and the Ancients.
Serra and Feroz tended this plane for some time as its guardians. Feroz, Serra's love, cast a magical barrier over the world to guard it from further despoil at the hands of wizards. Later Feroz died, and Serra left the plane in sadness. The countries of Ulgrotha then fell to inner conflict and Baron Sengir used this to tighten his grasp of fear over the plane.
Ulgrotha has at least one planar portal, which is located in the abandoned dwarven city under Castle Sengir. Where it leads is unknown, although we do know that Ulgrotha's dwarf population emigrated from beyond it.