We're not in a huge hurry to support QUIC / H3 given its current adoption. However, our users' apps will be able to support it once UDP is fully launched, if they want to.
Writing proxies is fun. Highly recommended.
We settled on Rust back when we were building a JS runtime into our proxy. It's a great language for hosting v8. When we realized our customers just wanted to run any ol' code, and not be stuck in a v8 isolate, we extracted the proxy bits and kept them around.
I think you could build our proxy just fine in Go. One really nice thing about Rust, though, is the Hyper HTTP library. It's _much_ more flexible than Go's built in HTTP package, which turns out to be really useful for our particular product.
I was actually just playing with Hyper for a few hours last night. Are you guys using async/await yet? Any suggestions for learning materials for async rust other than the standard stuff?
Ultimately I realized that most of what I needed from Caddy was really just certmagic, which has worked flawlessly since I got it set up. Plus I need the final product to compile into a single binary. Since my custom reverse proxy only took a few lines of code, I haven't worried too much about it. But there are a few features which I'll have to integrate eventually.
If I end up seeing myself headed down the path of making a full-fledged reverse proxy, I'll reconsider trying to implement my project as a Caddy plugin.