Understandably, some of the reaction to Pokemon X & Y's Mega Evolutions is the hope that everyone's favourite pocket monster gets the Mega treatment. Why not, right? Mega Evolutions are cool.
While not confirmed to have a Mega Evolution, if Porygon-Z actually gets one, UberAndrew has the best idea for it: it should be a callback to the infamous glitch Pokemon from Pokemon Red & Blue, Missingno. Porygon-Z, after all, is a cybernetic Pokemon. It would make sense! Observe:
How Missingno was made [UberAndrew]