I think this is a very cool project, but when I saw this statement, "Running Postgres at scale is hard. Eventually, one primary isn’t enough at which point you need to split it up.", I was reminded about this recent article about OpenAI, now one of the most visited apps/sites in the world, running on a single pg primary:

https://news.ycombinator.com/item?id=44071418

Quite from the article:

> At OpenAI, we utilize an unsharded architecture with one writer and multiple readers, demonstrating that PostgreSQL can scale gracefully under massive read loads.

Of course, if you have a lot of write volume this would be an unsuitable architecture, but just a reminder that pg can scale a lot more than many people think with just a single writer.