Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
Yep, I use MKV for the vast majority of my media. Mostly because I use MakeMKV as my primary disc ripping tool, but also for the reasons you mention about fantastic codec support. In addition it is great for storing multiple audio and caption tracks.
Dan Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.