>>267452118
Today is your lucky day

ffmpeg -y -i "<input file>" -f mp4 -filter_complex subtitles="<input file>" -movflags +faststart -vcodec libx264 -preset fast -profile:v main -acodec copy "./<output.mp4>"

Works on horriblesubs.mkvs
On mkvs/files with multiple audios or multiple language subs it'll die hard and you'll need to fuck around. 
I'll need to work on thing that is much better that works on anything.