I learned of one domestic airport implementing rapid testing, and the CDC wants them to somehow prevent anyone with a positive test from boarding a plane, which would for practical purposes require that the test provider notify the airline in question. There's some churn about HIPAA and privacy but I assume that will be resolved with a voluntary waiver.
After some discussion with friends, I'm thinking what might end up happening is there will be an app which will validate your vaccine status, but it could also alternatively validate a recent negative covid test... either/or, that would probably be close enough for government work.
Anti-vaxxers would still be able to do things like fly, but would just need a recent covid test. If many aspects of daily life require either a vaccine or recent test, they might have to get tested several times each week. Presumably tests would be readily available at work, school, etc and could be accessed via a common Db and app.
But I don't think that will get international pilots off the hook, we're all probably going to need the vaccine for most foriegn travel.