For the time being at least, most carriers have changed to only allow their own pilots to jump-seat - they will not carry other carriers' pilots that way. The FAA has also suspended their own OMC program for ATC. Several FAA employees I know were/are stuck in various locations after having flown there using the cockpit jump-seat. They now most return as a regular passenger seated in the cabin. I also ran into a UA pilot who had planned to jump-seat on Friday, the captain made her sit in the back.