YKA, KLM has already stopped visits effective immediately (as of the 12th that is).
Other airlines are certain to follow. For now the door is locked and bolted and the flightcrew will have to find different entertainment on long flights
There is talk in the US about armouring the cockpit doors as well as locking them. The materials under discussion are strong enough to stop a pistolround.
b.t.w., Dutch equivalent of the NTSB has announced it is opposed to locked cabindoors as it prevents cockpitcrew from investigating technical problems elsewhere in the aircraft (maybe they forgot to check on which side of the door the lock is, but they have a point