LoL. I can see that. I play the guitar, so it's just all the more annoying for me. XD
Actually the community has asked for it for a while, though not quite as fervently as other things. Personally I did want it but that was because of how LotRO handled music (Look up 'Weatherstock' on YouTube and enjoy).
In that game you used an emote, /play, to go into performance mode and then you could use the skill keys to play notes with the modifier keys to change notes. But they also incorporated the ABC file system to automate the process of playing songs where you could do '/play <songname>' and it would use the file '<songname>.abc' to play the song. The benefit of that being that there are also tools to take midi files and convert them to ABC files directly.
It meant you could record a song in midi, convert it and play it back in the game easily. But then Turbine is a US company, so there were the inevitable covers of copyrighted songs which SE can't afford to have happen as a JP company.