The Linux world often forgets that it's just a small part of the computing community. Just because Linux is not putting X11 front and center any more doesn't mean that everyone else is going to drop it like a hot potato. There are a LOT of internal enterprise apps out there that have been running on X windows for 20+ years, on those old standard war-horse Unixes (whose names I dare not mention for fear of starting a flame war), these apps (and the highly-paid consultants who write and maintain them) are going nowhere. X11 is going NOWHERE while there are still companies paying big $$$ to maintain their programs on X11.
Continued X development doesn't help these apps/platforms since it typically goes to new functionality and extensions which they don't use and never will.