LCA: The ways of Wayland

It doesn't include *every* xserver feature, but it includes every feature that can be used by normal clients. For example, you can't run a window manager that talks to a rootless Wayland-client X server and have it do much of anything. Wayland doesn't let arbitrary clients effectively lock the screen, so you can't stick with xscreensaver.

DRI2 and accelerations bypass the X server in the first place, so it doesn't matter whether the X server is a Wayland client or not for them.