During World War II, Hitler's regime forbade certain musical ideas and devices that didn't conform with their idea of artistic music.
From New Dutch Swing:
It [de jazzwereld's guideline for entertainment music in 1940] was mostly a detailed roster of forbidden devices and practices: plunger mutes, growls, smears and other dirty timbres, ostinato basses, background riffs repeated more than three times, charts written by black musicians, washboards, the use of the word 'jazz' were all off-limits.
How many of these devices and practices are parts of artistic masterpieces now? I bet there's even a washboard in a masterpiece somewhere. In the Great Courses lecture on Shostakovich, Robert Greenberg iterates countless ways that Stalin directly commented on and coerced the composer to conform to his ideals under threat of death!
What might a modern regime arbitrarily say is off-limits? Auto-tuned vocals? Sampling? Any music by someone whose parents or siblings were already rich and famous (not necessarily for music)?
I try to be careful not to rush to judgement on any broad musical device or concept, as one day it will likely be a part of some great piece of music.
Feel free to offer up any ideas of further musical elements that may surprise by going down in musical history. I will happily add them to this post.