Massive birdstrike would likely have dead birds all over the place, and this would have likely been reported by now.
Many years ago, a UA DC8 crashed while on approach to PDX (Portland, OR). There were only a few fatalities as there was no fire. And there was no fire because the plane ran out of fuel.
Premature, but I noticed that there was no apparent fire in this accident despite a plane that sustained some major damage. But if fuel starvation or depletion was a issue in this accident, I would find it unusual to lose both engines virtually simultaneously.
No question this will fascinate the aviation world in the days to come. One of the premier aircraft types belonging to one of the world's premier carriers crashes at one of the busiest airports in the world...