Go is tricky if you run on diverse platforms and want to do a lot of FFI, since cgo overhead is significant. The type system in Go is also not very powerful, which is both good and bad.

Haskell tends to hit performance walls that are very difficult to debug, and has a pretty similar learning curve to Rust (most people you hire onto the team won't know the language already).

The predominant competitor in this space is probably a high-level dynamic language combined with C/C++ library code. With good tooling and good practices to mitigate footguns, the extensive library support in C++ has a lot to offer.

Of course, I think Rust makes a better trade-off there, but early in the project it was not at all obvious that the good parts outweighed the fact that we would probably have been the biggest user of any library we depended on. We had some fun adventures in stress-testing HTTP/2 support here :)