Here is an article about recent updates by American and United:
United is offering fee waivers for travel through the end of 2020, and American covers flights through 9/30/20. There is a catch to United's new policy: travelers must make a decision and change or cancel their flight by April 30. (Travelers due to fly before May 31 don't have to meet this deadline.) Unlike United, American ticket holders don't have a deadline to decide whether to change or cancel their ticket,
I would expect that Delta will follow up with similar changes.