Color conversion from NV12 to RGBA or BGRA not working. Not supported by vaapipostproc and vaapisink

From what I can tell vaapi supports color conversion from NV12 to RGBA or BGRA just fine. I also verified this use case using libva-util (https://github.com/intel/libva-utils) without any issues.

Unfortunately both vaapipostproc and vaapisink gstreamer elements lacks support for RGBA and BGRA on memory:VASurface. (currently when using vaapipostproc to convert from NV12 to RGBA the result is an RGBA surface in system memory)

We would like to be able to build gstreamer pipeline using vaapipostproc for color conversion to RGBA(VASurface) followed by our own filter performing processing on RGBA(VASurface) on GPU.

Considering that vaapi supports this use case it should be possibly also support on by gstreamer vaapi package. Or am I missing something vital here?

Thanks, Petter