The article mainly concerns GNOME's plans, and Ubuntu aligning with that. Nothing worth a panic! 
Wayland will inevitably be the default, but I reckon X11 will still be around for many more years in maintenance mode.
KDE, the other big desktop environment, will support X11 session until Plasma 7. They split their compositor into two earlier this year, since one caused bugs for the other.
Since Wayland itself is just a specification, each implementation happens in the compositor (KDE = KWin, GNOME = Mutter) and I think the underlying toolkits need to support it too (GTK 3+, Qt 5+).
For MATE, I think it's going to be mate-wayland-session (based on Wayfire, inspired by Compiz)
Wayland isn't really a 'drop in' replacement for X11. Sure, it's modern, bit more secure, smoother with screen switching, but not perfect (yet). KDE keep track of "significant issues" affecting them.
I use X11 at home and Wayland at work. I notice subtle differences like:
- Both handle the mouse hardware settings differently (to do with DPI and the screen)
- On Wayland, I can't "menu roll" in GTK apps (click & hold the mouse button in a menu, and release on Save As to activate). Possibly a GTK or compositor bug.
- Some apps like colour pickers have inferior interfaces under Wayland.
I do personally prefer X11. 
The old timer's done so well.