If Vulkan is the future, we need to look at how one gets a Vulkan-based Qt application running on embedded devices without a windowing system (no X11, no Wayland).
The Qt Quick 3D porting work needs a real device based setup where at least Vulkan can be tested in addition to OpenGL ES.
What we should do first is to try creating something with VK_KHR_display. AFAICS i.MX8 (Vivante), Mesa, and NVIDIA (Linux only) support this. I have not been able to get it working with Mesa, though.