> The post mentions "The open source Deno runtime shows how clean and productive a modern, batteries-included, programming environment can be" so it sounds like they expect you'll be running database backed apps and not only static sites.
It suggests you'll be running a datastore, not necessarily an SQL database (the most overrated technology in existence IMO, especially for web apps where essentially none of its strong points are relevant). Storing old data as-is and migrating on read is definitely doable, and you can keep backwards compatibility to day 1 that way relatively easily. I worked on a system much like the one from "An oral history of Bank Python" that did exactly that, and had been doing so on a large scale for around a decade. Having a better-integrated datastore that can present multiple views of the same data is another way to achieve that, if you want to keep the migration out of the "application" code.
It suggests you'll be running a datastore, not necessarily an SQL database (the most overrated technology in existence IMO, especially for web apps where essentially none of its strong points are relevant). Storing old data as-is and migrating on read is definitely doable, and you can keep backwards compatibility to day 1 that way relatively easily. I worked on a system much like the one from "An oral history of Bank Python" that did exactly that, and had been doing so on a large scale for around a decade. Having a better-integrated datastore that can present multiple views of the same data is another way to achieve that, if you want to keep the migration out of the "application" code.