When the first iPod came out, it didn't have feature parity. No wireless, no FM radio, smaller drive, no Windows compatibility. But it was better at the important tasks (finding music on your library, controlling playback). Similarly the first iPhone OS was missing quite a few features compared to BB/WinMo.
If Wayland or Mir can do a better job for the 80% or 90% case, they could easily displace X11. The fact that they are cleaner codebases (since they aren't 20+ years of layers) means they can probably respond to new use cases or important gaps faster than X11.
Which is why there has been so much fuss. I haven't kept up, but has the Wayland project changed their tune on networkable graphics? I will grant that X could use some uncrustifying, but I think the general gist of the OP is correct: there is just so much that X offers that Wayland and Mir will have to catch up to (assuming they can, which requires not just time and effort, but forward thinking on design and architecture).
And as for performance, my N900, a four years old phone, runs X just fine. The sad experience I have had with software (including OSS), is that the newly born projects are almost always designed without paying attention to efficiency, usually through a lack of awareness because people are so used to fast hardware these days.
People run crapburgers like GNOME and then say "X is bloated and slow, we need to replace it NOW with Wayland". Uh, no, your DE is bloated and slow. X is warty and certainly worthy of criticism, but force-switching everybody to PulseVideo--sorry, Wayland, is not going to solve all the problems with the Lunix desktop and is going to introduce a whole new slew of transition-phase problems.
As you said, Wayland actually provides less than X. If you want to turn Linux into Windows, then the solution is a single, standardized, soup-to-nuts graphics layer incorporating everything from graphical primitives to widget toolkits and user-interface guidelines. Linux still has multiple toolkits and multiple DEs squabbling for mindshare, and seems to grow one more everytime GNOME pisses someone new off.
You mean "provide a flag in ssh to forward a rendered window?"
They were talking about having hooks so a VNC server could act as a compositor for windows that it can forward over the VNC protocol. That would be a much better solution than raw pixel buffers like X forwarding had.
In Wayland, I can easily see the ability to run an X server on top as a motivator, but in the end the killer feature needs to be performance and a tide of new software targeting EGL / WaylandInput insteaf of GLX / XInput.