Even if this is true, isn’t that about drivers and not interfaces? Perhaps I am wrong but I was under the impression that the framebuffer userspace device worked on DRM-based drivers still, just it didn’t use fbdev internally.
DRM has a thing called “dumb framebuffer” which exposes a memory mapped file with the CPU-accessible frame buffer data. See DRM_IOCTL_MODE_CREATE_DUMB and DRM_IOCTL_MODE_MAP_DUMB IOCTLs. The only inconvenience, some boilerplate is required to find the correct GPU connector, and setup a supported video mode.