I have tested it out and mkv files Do indeed work. It is cool to have the ability to take a hash and stream any video through mpv or whatever you use.
I get the feeling that purevidz is moving into not just a streaming service, but also an IPFS Media DataBase, which I don't think anyone currently has. Also, its acronym is IMDB, just an interesting find.
And to he guy above me, webtorrents is in beta and IPFS I think is still in alpha.
Sidenote, don't try and upload videos through the web app for IPFS, in the examples section is a clear way of uploading video through the terminal which works.