Full disclosure: I have no relationship to planes so I bow down to you gods, I am but a lowly analyst who has studied threat groups as part of my work.
Any organised terrorist group would have claimed their prize by now as not to do so would be unproductive in their misplaced eyes to their cause.
I wouldn't take this off the table so fast. In this day and age people seem to only remember the kinetic actions of these threat groups. Terror groups work on fear which by the looks of things this event has avoided. Maybe the passengers are now hostages who will be used as bargaining chips to trade for captured comrades. Maybe this could happen again which then would put people on edge.
Perhaps they are waiting to get into a secure location before making any comment or taking their next action. Particularly in the short term there is no rush to claim responsibility.