The organisation I work for has just obtained approval to operate Ipads in the cockpit.
It was limited to one model, with the transmit/receive set to a particular mode, subject to retention tests on the mountings in the cockpit at predicted crash loads so that they can't do damage to people in such an event, and getting all that approved cost us a couple of tens of thousands of pounds.
And they're great! But to extend that easily to a wide range of pax devices would be impossible.