Dude! We're trying to brainstorm...
Hm, how about this. A highly charismatic Randian/Libertarian Social Darwinist convinces pony society to try out a "rule of the strongest" society and forsake the parenthood of Celestia. They "kill the Mother" so to speak, and emancipate themselves. It is an era of great pain and violence, but also of exhilarating freedom and opportunity. Equestria isn't a Sugar Bowl anymore, but it's a world of unbridled madness and awesomeness. Cyborgs are just one of the forms this madness takes.
In this climate, Rainbow Dash starts out as a mere weather manager, and... somehow ends up a bloodthirsty overpowered vigilante goddess of war and awesome? I think Awesome and Loyalty would be the key words here... the Arc Words even.