As much as I don't like "Friendship is Witchcraft", it got me thinking... what if... ...what if it WAS the real Cadence all along? If Cadence really was just stressed out from the wedding? If it really was just a way to reinforce Shining Armor's protective shield? I mean, Twilight hasn't seen Cadence since Twilight was a filly. People (Ponies, whatever) change over time, they often are not how we remember them as children. How would the rest of "A Canterlot Wedding" would have played out?
Then Twilight would have been uninvited to the wedding. Her actions would have destroyed her relationships with her brother, Cadance, and Celestia. Her friends would have started to distrust her more, and it likely would have ended those friendships eventually. In the end, Twilight would have ended up sad and alone, having lost everything and everypony she ever cared about.