There is no choice but to do the alternative: modify and modernise all our critical systems piecemeal over decades while they are running, covered by the business cliche "We are building the plane, while flying it."

We all naively desire (especially politicians) the software concept of the big rewrite, the version 2, project phoenix, Second-System Syndrome. With development experience we learn both the psychological pull of the concept and we learn why it is so hard to do successfully. It always seems so simple how to fix societal systems we have no experience with.

Successful systems slowly improve, slowly introduce and prove new ideas, slowly accrete changes: we accept the costs of vestigial path-dependent aspects and technical debt.

One of the incredible learning experiences of developing software systems is that it is a huge melting pot of different techniques that are iterated quickly (fast parallel evolution and proving) and the knowledge diffuses between people and teams and organisations. The waterfall model is rarely used! I believe we are now seeing those skills and techniques be applied to other system domains - especially high growth businesses.