It'd be nice to lift out Chromium's own network stack into a library (as a continuously-rebased-from-upstream derivative fork), and then build a proxy that made requests using said network stack. Then you'd get all the HSTS/cert-pinning logic, the CORS and only-N-requests-per-host-at-a-time policies, and a very good LRU cache implementation, "for free", for your proxy daemon.

Heck, if you don't mind an extra 100MB of memory consumption, you could probably throw a "correct" proxy-daemon together in Javascript by relying on the browser network stack of a [headless] Electron instance.