Well, not the only one. I tried to implement X11 EGL platform in libhybris. Basically it implements custom ANativeWindow, which renders to gralloc-allocated buffer and then outputs image via Xlib. It's not very fast on FullHD device due to doing multiple copies and X server itself rendering in software, but works as proof of concept and faster than LLVMpipe renderer on same device. Photo.

I had to start a normal Xorg server on framebuffer though instead of Xwayland. The problem is that hildon-desktop seems to expect the device to be in tablet orientation initially, and behaves weirdly in portrait one, which is the default for lipstick (SailfishOS Wayland compositor).

It's also possible to add custom Cogl backend which would connect to both X server and Wayland compositor, composing windows from the first and rendering through OpenGL to the latter. I tried similar hack with Android's SurfaceFlinger instead of Wayland before.