To be clear: mainstream major media publications use anonymous sources all the time. The point here is that the whistleblower be talking to the Times or the Post[1] and not "View from the Wing". No one is demanding they come out in public to tell us who they are.

[1] And let's also be clear: journalists from both those organizations are surely on the phones full time right now trying to find dirt on Boeing quality processes. That would be a huge story if they could land it.