Currently on my Vizio M70-C3, the plex client is transcoding 1080p HEVC 10bit and 4k HEVC 10bit content to 1080p h264 8bit.
The TV is perfectly capable of playing HEVC 10bit and can do so via the DLNA client. Ive tried changing the opera profile to support this format but it always decides to transcode. There is much more 4k content available now in 10bit then in 8bit hevc. To further add to this fire, the DLNA server times out when viewing a folder with any reasonable amount of files in it. This makes actually using the DLNA client to watch 10bit content even more difficult.
I should also note that 4k images through the plex client are also converted into 1080p... infact the only thing this plex client has ever successfully played as 4k is a h265 8bit mkv file.
Vizio Sigma 1.3.15-UHD