Subtitles are the biggest non-issue it's crazy... Some devices don't support internal subs, so you just extract them for your entire library using ffmpeg;
pushd "\\nas\Media\Movies\"
fd -e mkv | each {|x| ffmpeg -i $x -map 0:s:0 $x.srt }
Once it's done, it's done forever for the files you have. As you add them, just run it again.