If Google were to start over, all of that would be thrown out. It just can’t be done.

To stress the importance of this very basic fact, people need to understand that even Google, a company with virtually limitless resources to rearchitect and rewrite any and all type of software project, made the call to avoid using major features offered by some programming languages, such as C++'s exceptions, because it could have unintended consequences on the company's legacy code base which they could not rewrite.

And here we are, reading fantastic claims over how complete rewrites are reasonable things while flipping compiler flags to harden legacy projects is unheard of.