The crazy thing is that the Pages router looked to me to essentially be a React flavored version of the venerable Perl HTML::Mason library.

It offered embedded code that is used to generate static HTML server side. It had application routing based on the file directory structure of the repository. It had automatic code wrappers distributed across the directory structure.

https://metacpan.org/pod/HTML::Mason

I used the heck out of HTML::Mason for years and it scaled ridiculously well to large apps.

Over time, HTML::Mason was supplanted by Mason, but I never used it due to not working in Perl anymore.

https://metacpan.org/pod/Mason

If you like the Pages router, it wouldn't hurt to dig through ancient scrolls of Mason users to look for techniques and lost knowledge.

Caveat: I haven't written or maintained any big apps in Next, but I've played with it a bit and have supported the SDKs I work on in Next apps.