I would bet on prop control failure depriving capt of reverse, or enough reverse. But we'll see.
New reg coming, I would think--"stay seated till vessel is stopped, don't line up early at the exits" or the like. Downtown New Yorkers will hate this..
A lot of commercial vessels use variable pitch propellers for both speed and direction control. Failure of the control mechanism can have serious results.
I was on a MODU (Mobile Offshore Drilling Unit - ie jackup oil rig) when the supply boat lost control - the props failed in full reverse pitch. He went right under the rig, bounced off the bow leg, gave us a good shake and punched some holes in his side, fortunately above the waterline.
I can just imagine something like that happening with a ferry full of people...