Imo Immemorial Glade is the best mechanic Gabe have ever done, it's just so cool and interesting that you hardly believe to witness something so inventive in this type of games.
Un-very-fortunately, it's one of a kind by now, so, unless Gabe will be willing to get some more headache to create something similar, this is it to the mechanic. =\
As for this location in the "real world", it is barren and will be barren till some endgame I suppose, because it's just lame to reveal what's behind that door now, since it's clearly connected to that warp world and can potentially contain something very big.