Cap'n Proto is relatively new, so yes, the tooling is less mature than for more established protocols. We've been making steady progress, though, and things are definitely usable right now. E.g. CloudFlare is reportedly using the Lua and Go implementations in production.

Perhaps you're interested in helping? We love new contributors, and I can personally attest that writing an implementation of Cap'n Proto is a great way to really get to know a language. I've been waiting for someone to jump on Swift...