[csytan]

This pattern was taught to be by a former mentor, except he phrased it "always be ready to ship". I used it to convert my app from rendered HTML + jQuery into a full fledged VueJS app + API. Much, much better than rewriting.

One more thing to add, is that a lot of software (e.g. SAAS) has users that depend on it. You want to make sure that your customers are happy through the transition.