This is already the way OnLive, for example, works. All the rendering is done on the server side, which corresponds to the Wayland/X11 client.
However, even smartphones are coming with highly capable GPUs these days, so within a few years, any CPU no matter how cheap will be able to handle at least casual gaming at HD resolutions.
Remoting isn't as important when you have options like VNC to fall back on. Its a minor inconvenience at the most and I believe the've made the right call to ship something usable now.
Regularly, I have to give support to portugal or italia, they open a internet connection, so that I can log on their system. With a simple ssh -Y, I can perform all the investigations I need.
I have NoMachine NX on my home computer. It is very useful, but it is far more heavy weight than a simple ssh with X11 forwarding.
Some people claim it depends on adequately configuring X, which may be true, but it's much easier to configure VNC over SSH to have an acceptable performance
On Windows or OSX though... If you were going to install X11 why not skip it and just install VNC?
VNC is no alternative for running individual applications remotely. Remote desktop != remote X.
Still, most of the time, running only one application is not the usage model. Or it's a simple thing that doesn't need X, just ssh
[1] Yes, I know there are exceptions.
X separates the thing that paints the screen (the X server) from the things that computes (the X client).
Your idea or pushing pixels means that you need a virtual screen on the machine where programs runs and you want to copy this virtual screen to your screen. Do you imagine the complexity of window management with such a setup ? Have you already launched many VNC clients at the same time ?
"Screen for X"
If you need remoting, for probably a fairly long way into the future, X11 will still be supported and you can use that. If you want the new shininess of Wayland, sorry, you have to live without remote capabilities.