Well, it's never clearly stated, but Tsars Ivan Asen and Peter of Bulgaria (12th century) could have been pretty low-class by Byzantine standards. Eastern Europe would have been the easiest place to generate a successful peasant's revolt, despite the more famous stuff in Western Europe. You generally had weaker states there and more linguistic, religious, ethnic divides etc., the sort that would motivate peasants to revolt.
A well-timed peasant revolt in Albania or Macedonia during the Great Turkish War might also have been supported by the Austrians, at least for a couple generations or so.
A Swiss peasant uprising would be my best pick for Western Europe. No major threat to any established order, very poor, and terrain that vastly favors the defence.
The example won't be followed, and states won't become more repressive - for if European leaders feared the influence of the peasant revolt, they would have chosen the comparatively 'easier' route and crushed said revolt entirely.
Re: Mello, I think there was absolutely 0% chance that the Jacquerie could have succeeded. No king could take the risk of having peasants rule any economic place of even mild importance - the contagion risk was too strong. And the Paris region was a rich and strategic province, no less.