Well a Vmca departure could also lead to a wing stalling if you try to keep the nose up and try to counteract with ailerons plus spoilers.
I know that with full power on one engine only if you allow the speed to go below Vmca on a Dash 8 it will roll into the dead engine pretty fast.
Of course if you keep bleeding the speed back then the wing will stall most likely the one with the failed engine first because of the prop wash on the other wing.
In this case it could be that they initially thought they could make the opening on the other side of the highway but at the last minute saw they could not and added power (if it wasn't always at max power) and were too slow and hit Vmca.
Anyway with the black boxes retrieved, they will know.
Obviously an aircraft not under control both in direction, speed and altitude.
