Nice idea but terrible implementation. Mitmproxy solves a lot of annoying problems, but, Python holds it back to such an extent that it's hard to make the case for deploying it in production due to massive inefficiencies.
I thought mitmproxy was designed to make it easier to debug stuff in a local environment. Why would you want to deploy it to production? How would you use it?
One of the things I like about mitmproxy is how easy it is to develop and use addons. You just pass a script file to it. How would you achieve such painless extensibility if it were written in Go?
It's very hard to do with Go; also see Hugo, where Go is in many ways "holding it back" compared to something like Jekyll, which you can customize and hack with great ease.
I love Go, but this kind of things is not where it shines.
mitmproxy is explicitly intended as an interactive MITM for debugging: "your swiss-army knife for debugging, testing, privacy measurements, and penetration testing".
What you're talking about here was never a goal. And being in Python means it's much easier to extend, which is also greatly useful.
FWIW: I'm building something in Go (https://github.com/dstotijn/hetty). But it's pretty early stage and not even near the featureset that mitmproxy or Burp Suite has. Also I wouldn't dare say it's more efficient (yet!). But Go has been great so far to build it.
As mentioned elsewhere: (dev friendly) extensibility/add-ons with Go will be an interesting challenge. Haven't looked into it yet.
Can't wait for someone to do it in Go.