Several times since BW, a Decepticon/Predacon has switched sides & become a good guy. I can't think of a time that the reverse has happened (on screen) where a good guy has switched sides & gone evil. There has been a few that happened off screen in the past (Armada Wheeljack, Animated Elita/Blackarachnia, Animated Wasp) but not a story line showing a character as good, the choices being made, slowly becoming more evil & finally, on Megatron's side. And of their own choice, not some programming error that causes them to be evil. Reason for this thought is in the recent Prime ep, discussion about it as seeds being planted of Breakdown possibly pulling a Dinobot. While I can't see the current cast of Autobots doing this, it would be cool to introduce a new cast memeber & have them go evil. Maybe they just don't share Prime's views on how they conduct themselves & maybe a few run-ins with Mech lead the bot to begin to hate humans.