If the USSR had taken the approach of Tito's Yugoslavia, they could happily have absorbed every Western popular genre from Megadeth to Boy George and not have endangered themselves in the least. Yugoslavia gave the impression of being more liberal because of that sort of openness, but anyone trying serious political opposition soon found they were actually tougher than Krushchev or his successors when it came to the crunch (I knew someone who did time on Goli Otok for a trivial political offence - not fun at all). A Communist regime that took the trouble to distinguish empty gestures from genuine threats could easily classify them accurately.

So, as what-ifs go, Lennonism never had a prayer of supplanting Leninism.