Main problem is that a proper UHD movie is between the 82-128mbps if you include the Atmos/DTS-X audio and every TV model only supports a 100mbps LAN cable.
Then you need to stream it with wifi to still achieve these speeds but that can sometimes be unstable or downscale the movie with the live transcoding plex offers.
Above the 100mbps your direct stream to the plex app on the TV will be forced to keep buffering and in this case being able to downscale it but preserve the HDR would be awsome.
That is also the case for people who want to stream something on a HEVC supported device and are on 4G or a bad wifi, you should get a better quality stream on your device with HEVC than H264, lower bandwidth, higher quality. I think it will also preserve the color of the stream than whitewashing it because of the 10bit color -> 8bit color when it is transcoding HEVC -> H264.
