Henadic Theologian
Legend
Looks like Exandria is off the list
I still say it could be Greyhawk
What else has a bit of ink spilt for 5e? Planescape and Spelljammer for sure.
None those could be revisit, but they could be one of the "classic" settings.
But your right about Exandria being out as a possiblity thanks to CR self publishing the new CR book. Exandria was the one competitor to FR for being the return setting, so yeah its 100% certain, but resent events have sucked all the joy out of it for me.