The next problem is the testing infrastructure. Few labs (if any) do PCR tests with results guaranteed in the next 72h in major US cities.

What if test results are late? Should you delay and take the first flight after getting the results? Now the test was taken 4 days or more before the new flight. Should You take another test?

Airlines or countries that do not want to welcome travelers without a recent, <72h PCR test should set up the necessary infrastructure in the city of the departure airport.