Isn't the real problem recompiling executables for which the source is lost or are so hopelessly mired in legacy production systems deploying them would be hell

Isn't the real problem recompiling executables for which the source is lost or are so hopelessly mired in legacy production systems deploying them would be hell on earth. That was the basic problem with Y2K no one expected them to live that long so upgrading them wasn't considered. This seems like the same retrofit issue, possibly with more warning and experience second time around.