Or for that matter XFree86 / Xorg and Xlib have aging issues. IMHO the protocol is okay (it's not perfect). Maybe cut away some of the legacy cruft, implement antialiased rendering for core primitives (yes, even if they are just lines, arcs and ellipses, those are still needed even on modern screens; heck with all the flat style UIs currently being all the rage on a HighDPI screen you could probably disable XRender and nobody would notice).
The whole framebuffer handle management of Wayland is a huge step in the right direction, but I despise Wayland's input and inter client communications model; not to say that X11 was anyway better, but whenever I code against Wayland, that part feels just wrong. Also the obsession of the Wayland devs of getting VSync right has its own share of issues (especially for low latency graphics, like you need it for VR).
And agree with the author. X11 has aging issues.