Your question reads as slightly tongue in cheek. But you can learn something by asking and answering it in this case. When should you think about rewriting some

Your question reads as slightly tongue in cheek. But you can learn something by asking and answering it in this case. When should you think about rewriting something? 1. When it's a common recurring source of bugs/problems/pain. 2. When it's no longer fit for purpose. Often either because the purpose has changed in some way or because the purpose was misunderstood when it was created. In this case at least some of the rewrites were prompted by subsystems being a common source of memory safety bugs continually popping up. Rewriting with technologies and techniques that eliminate some classes of memory safety bugs immediately and in the future is a pretty large payoff for a kernel.