All plausible scenarios, Vmca excursion, Dual flameout, or incorrect securing of a non-failed engine.
I'm tending to think they had lost power on both power plants, because if you look at the speed/graph posted, when the aircraft stopped climbing, it was in a very steady descent, with mostly constant speed.
Seems to me that badly mishandled asymmetric flight would at least provide mostly level flight, or at least a shallower descent. That last minute pull was an automatic reaction to the pilots seeing that they were gonna hit the bridge or power lines. I don't think it was a Vmca roll, it just doesn't seem to have enough yawing and the wing drop looks more as a result of a stall.
Either way, the recorders look in great shape so we should have all the data soon and I'm sure the preliminary report will be quite expedient due to this airline's safety record. This will be a very politically charged event no doubt.