I only glanced at the docs, but way they expect apps to integrate with it seems a bit convoluted to me? It's not really a reverse proxy at this

What would be wrong with just using HTTP/2, maybe with a few custom headers sprinkled in for custom features?

> It's not really a reverse proxy at this

In fact it's not one at all, nor does it claim to be. It's an app server.

> NGINX Unit – universal web app server – a lightweight and versatile open source server project that works as a reverse proxy, serves static assets, and runs applications in multiple languages.

https://github.com/nginx/unit