Gangplank and Miss Fortune available now

I have a question regarding Miss Fortune.

From what I have read and recently played regarding her kit update, I'm a bit confused as to what Riot had planned for her.

She has what I would call......"Corki Syndrome." But to a higher extreme. Corki is a little problematic as an adc, since most of his scaling (until somewhat recently) was based on AP for three of this skills, and those three also dealt magic damage. Miss Fortune (post update) has both AD and AP scaling on her q, AD for magic damage on her w, AP scaling on her e, and incredibly confusing scaling on her ulti.

While most of this has been part of her pre-update kit, the ulti scaling is really what leaves me baffled. Build ad for magic damage? Build AP (which is generally a no-no for marksmans) for physical damage? On top of that, her recommended build involves getting a lot of armor pen (black cleaver, last whisper) which is utterly useless aside from her ulti/q's base damage and her autos.

So, Riot, how should we really build mf? Because at this point, I'm at somewhat of a loss.