I just got my shipment of both books today and have skimmed through them. What caught my eye the most was the little sidebar in the tabaxi section titled "Tabaxi in the Forgotten Realms":
"In the Forgotten Realms, tabaxi hail from Maztica, a realm located far across the ocean west of the Sword Coast. The tabaxi of Maztica are known for their isolation, and until recently they never ventured from their homeland. The tabaxi say little of why that has changed, though rumors persist of strange happenings in that distant land."
This really sounds like it is setting up a future AP in Maztica. Yuan-ti temples are also very Central/South American in build, so they could be the antagonists for this. A SCAG-type book and an AP in Maztica would be very cool.
Also, whether it means anything or not, in the Distant Lands section of Dungeonology, Kara-tur and Al-qadim are mentioned, but not Maztica.