Does anyone have any idea when Direct Play for MKV files will be supported in Plex without needing to transcode? I would love not to have to use handbrake turn mkv media into mp4/m4v.
It already is supported. Remember though that MKV is just a container. What matters are the video and audio streams (and their codecs).
The problem you’re seeing may be because of your client, or issues with your MKV containing unsupported codecs for that client.
This totally depends on the client you are using. Plex Media Player/Plex Home Theater will direct play with about any media you throw at it. For other clients it purely depends on what they support by themselves.