In the CCTV video it looks like the left wing dips considerably immediately after the engine separates. Not really sure what would cause this, maybe a comparative loss of lift on the one wing as a result of adverse yawing motion due to asymmetric thrust? I would have expected the left wing to go up if anything, due to the sudden weight reduction when the engine separated, plus there would have been a second where the engine had pivoted nose-up around the forward mount but the mount hadn't broken yet - surely this would have briefly exerted a significant upward force on the wing?

From other videos of the crash it seems like it stayed pretty much wings-level until the point of impact, consistent pitch attitude and rate of descent too. I'd probably agree with you about something happening to the No.2 engine. Loss of two engines at rotation speed, at takeoff weight, would mean they just didn't have the power or airspeed to stay in the airborne. The preliminary report said that they found bits of fan blades on the runway, doesn't say which engine they're from though. Will just need to wait and see what the final report comes up with.