Provided that the In Flight Entertainment can be interrupted on the ground to run the Safety video and hence ensure pasengers wearing headphones will hear the demo, or can be interrupted anytime when PA announcements re made, regulatory approval for allowing headsets to be worn during take-off and landing can be authourized.
Over the ear earpieces are usually joined by a headband forming a closed loop which could conceivably trip folks up in the event of an evacuation. Use of these type is not allowed during T/O or Ldg.
Earbud types headsets hang at the end of a cord and arent connected by a headband. You can use these anytime.
The only other safety issue I'm aware of re headphones is that seatback IFE systems are becoming mainstream and the standard for the earphone jacks on these new systems needs to be beefed up or made mopre robust. The new systems being installed have jacks that are shorting or failing quite regularly and people are receiving minor shock/burn type injuries.