A "hobbit" makes an appearance the 1989 game Curse of the Azure Bonds, even though halfling characters are possible and there's an important halfling (named as such) earlier in the game.
All that's needed for Planescape is a follow-up Manual of the Planes type book, and at that point, coverage is pretty complete. It seems that the vast majority of people knew that there simply wouldn't be a way to do complete, full, in-depth coverage without a book that would need a wheelbarrow...
The various mentions of the various Mulan deities wasn't in any organized manner; it was much more off-handedly. Also Isis and Osiris weren't mentioned either, and they should have been. It was all very ad hoc.
We kind of need a sister thread to this one: "What areas should Adventures in Faerun II: Elminster Boogaloo cover in detail?"
I've often stated that Cormyr should have gotten in-depth coverage in this book, as well as Thay. Let's hope it does well enough that we can get a sequel covering...
The only mentions of anything outside of Faerun proper by name that I've found so far is a mention of the Hordelands. Granted, there's a lot of reading to be done.
As part of a suggested outline for a Dalelands campaign featuring Moander:
"Levels 17–20. Moander manifests as a Blob of Annihilation to enter Myth Drannor and feed on the ancient magic of the broken city, becoming even more powerful."
I mean, that was basically his plan in the novel, but I...
As per page 238 of the PHB, all spell targets must have a clear path from the caster and can't have Total Cover. Which would make the first problem go away, although a magical scout is still a possibility.
It's been about a decade in-universe since we've had any updates, which seems to be that Unther conquered the the rest of Tymanther other than one city, and many dragonborn went to Calimshan as mercenaries.