Just a reminder that even though the tunnel itself is encrypted, the whole connection is not E2E encrypted between your remote client and the server. Cloudflare as a CDN/PoP provider can see the traffic in plaintext.
In all other aspects, this is a great solution, as we even get to use the edge caching(over top of all others mentioned above) facility - which further reduces the requests to origin server.
Few things which makes achieving reproducible/deterministic builds hard are - timestamps of generated/compiled files, continuously updating versions of build tools(+support libraries), output binary difference compiled across different OS.
We can use docker based build system for this, but it would require very carefully configured Dockerfile to keep the build tools+libraries on specific version. And if we do a pre-built Docker Image, then the Reproducibility of that Docker Image has to be proven first. It is indeed a difficult task, but not an impossible one. With F-Droid providing a sound framework for reproducible build generation, I believe we would have majority of large Android Apps reproducible in next few years.