NetBSD: Wayland Has Moved Away From the Modularity, Portability, and Standardization of the X Server
Recent: OpenBSD Founder Theo de Raadt Says Wayland is an Attack Software Choice and a Push Towards "Vertical Software Monocultures" | OpenBSD Says That Even on Linux, Wayland Still Has a Number of Rough Edges (But IBM Wants to Make X Extinct)
What NetBSD says about Wayland:
In a Wayland system, the "compositor" (display server) is responsible for managing displays, input, and window management. Generally, this means a lot of OS-specific code is contained there.Wayland does not define protocols for features X11 users expect, like screenshots, screen locking, or window management. Either you implement these inside the compositor (lots of work that has to be redone), or you define your own protocol extension.
The Wayland "reference implementation" is a small set of libraries that can be used to build a compositor or a client application. These libraries currently have hard dependencies on Linux kernel APIs like epoll. In pkgsrc we've patched the libraries to add kqueue(2) support, but the patches haven't been accepted upstream. Wayland is written with the assumption of Linux to the extent that every client application tends to #include <linux/input.h> because Wayland's designers didn't see the need to define a OS-neutral way to get mouse button IDs.
So far, all Wayland compositors but swc have a hard dependency on libinput, which only supports Linux's input API (also cloned in FreeBSD). In NetBSD we have an entirely different input API - wscons(4). wscons is actually fairly simple to write code for, someone just needs to go out there and do it. You can use my code in swc as a reference. :)
In general, Wayland is moving away from the modularity, portability, and standardization of the X server.