Waypipe has nothing to do with the kernel mode setting driver. The X server code does not run in the kernel. Wayland compositors use kernel modesetting for mode changes, so not sure what your point is? Not saying you need to switch to Wayland, just saying that it covers the use case you described as impossible with Wayland.
If that is the case, then you can probably easily find the X server code in the Linux kernel and send a link? Spoiler: it is not there