The standard “hello Wayland” project[1] is basically that, using an interface called wl_shm. You still need to do some IPC in order to arrange for the environment to so that for you, obviously, so a library called libwayland-client handles the necessary Unix socket handshake, plus some more of that to tell the system you’re done with the buffer and want to submit it. It would be possible to isolate the first part into a reusable executable that performs it then execs you leaving a mmapable fd for the buffer, but the second you’d still need to do yourself. (Wayland isn’t willing to just use a pixel buffer you’re still writing to—indeed I don’t think GPUs can do that as opposed to requiring an explicit transfer to video memory.)

[1] https://github.com/emersion/hello-wayland