I think its a bit early to speculate.  The investigators have a lot more information than the rest of us, and they won't announce a finding for months.  As with most plane crashes, there probably was more than one problem, a sequence of events.  The first may have been the ice issue, but that alone wouldn't crash the plane.  Perhaps the tail de-ice boots were not functioning, perhaps the pilots did something they weren't supposed to.  The media was quick to hang the pilots for using the autopilot, however the book only recommends turning off the autopilot in extreme icing, which supposedly was not the case.