You know, strangely enough, a sonic rainboom is pretty much the one flight trick that doesn't actually require wings to pull off. Rainbow Dash wasn't flapping her wings while she was diving downward, so presumably she was accelerating through purely magical means.
Then again, maybe a pony still has to be a pegasus for that, depending on how that flight magic works, and they still wouldn't be as good at it as Rainbow Dash. Plus even if Rarity did manage to do it anyway, turning is still gonna be a slight problem. But it'd sure be going out in spectacular fashion, at the very least.