I think the FTSB said it could be up to two years before they make up their minds what happened.
It's one giant body with an itsy bitsy brain at work, a dinosaur waiting on a meteor to hit.
I think NTSB will get a report out on this one fairly quickly since there is so much evidence available, including a fairly good fuselage and powerplants. Good weather, lot's of eyewitnesses, aircrew, videos, black boxes, etc. etc. Two years would be ridiculous given all of the above and the aircraft manufacturers and the airlines would be in an uproar if they're left hanging for two years with no good reason. I's expect a comprehensive preliminary report fairly soon.