> It’d be VERY cool to make materialized views straight from the log!!

This is what Materialize does. You point it at some PG (or MySQL, or... probably lots more by now) sources, and then you can define arbitrary views on top of those sources using SQL (with the full power of relational logic: fully precise joins, etc.) The views are maintained incrementally, so they update almost instantly when the underlying data updates; you don't have to manually refresh them.

Disclaimer: I worked on Materialize for five years, and it is a commercial, proprietary project. But it is source-available (https://github.com/materializeinc/materialize) under a BSL-style license, and it has fairly generous terms for free usage.