WTF are you talking about?? All official Warez group releases are in .mkv format. MKV never went away.
It's 2016, if you don't have a devices that can play .mkv files you already losing.
nikkas are really re-encoding their .mkv files into .mp4 files or changing the filesname in 2016.
If y'all wanna convert a .mkv file to a .mp4 file, y'all need to download & install ShanaEncoder. It'll allow you remux/stream copy a .mkv file into a .mp4 without reencoding the file.
Here's the link on how it works & simple instructions (this is where I learned about it):
How to Rip Blu-Ray Videos: Part 2 - Remux MKV to MP4 - Thurrott.com
Here's a link to go downalod it:
ShanaEncoder 3.2 - Download