Did you read the article at all?

“Putting all new code aside, fortunately, neither this document nor the U.S. government is calling for an immediate migration from C/C++ to Rust — as but one example,” he said. “CISA’s Secure by Design document recognizes that software maintainers simply cannot migrate their code bases en masse like that.”

Companies have until January 1, 2026, to create memory safety roadmaps.

All they are asking for by that date is a roadmap for dealing with memory safety issues, not rewrite everything.