From that link: Once Mir’s support for Wayland clients is on a par with the support for “native” Mir clients we will likely phase out support for the latter.
Does that mean they want to phase out Mir once they have a full Wayland display server? I thought the whole point for them was to continue to support those that are already using Mir? This still doesn't make any sense to me.
I thought one of the original distinctions was that Mir was going to work with the old closed-source nVidia driver, while Wayland insisted on doing it the "right" way and made nVidia catch up instead of pandering to them. Other than that, I've never heard anything to justify Mir's existence. Why not just start with an existing Wayland server that supports all the features and move on? They'll reach the end goal faster.
I'm not trying to be negative, but if the end goal is to be a Wayland display server then why is it so hard to let Mir die? Is it just pride? Separation Anxiety? ;-) j.k. but really what is it?
What existing wayland server? Gnome and KDE has it's own, there was not a generic server when Mir announced support for Wayland and from what I know some people are working on creating a library that can be used for creating compositors, Mir is a solution for DEs like Mate because it would be easy to work on using Mir as a server so gaining wayland support then doing a compositor from scratch or using a library.
It was always obvious to me that Wayland was the future replacement for X for a long time. Why they had to take the ideas in Wayland and do something a bit different in Mir has always been a mystery to me.
There is no separate display server in Wayland. The window manager fulfils the roles that a display server would, using the libraries provided by the Wayland project.
Some of those are DE specific, especially the Gnome one,btw Gnome announced that they need to rewrite their code again it is wayland and X related so you should search and read that post if you missed it.
I do not know all in the list but the Weston is a testing ground, not intended to be used as it is, some like Sway are full WM+compositor, Mate could not use it.
I think it is a good idea to have a generic server that implements wayland, implements all the missing extension and all small DEs can use it if the user wants Wayland. Also Mir would continue to be used in IoT and other devices.