Or you can run postgres on the same machine as the application, which lets you much more easily migrate if the time comes when you need to scale to multiple application servers.

There's a world between "local file" and "network DB server", running a DB server locally has lots of benefits from being able to easily query from outside if needed to forcing you to consider concurrency without the latency overhead of a network hop.

This decision tree doesn't make much sense to me. Why you someone forego performance today in favor of adding a completely unnecessary network layer to every DB query in order to "satisfy" future imaginary "scaling concerns"?

That's still orders of magnitude more complexity for no real benefit. A migration from sqlite to postgres, if really required, is not that hard.

Now you've added a substantial dependency, and annoying setup requirements. Good luck doing this for a native app on mobile or desktop.