Cap'n'Proto is extremely cool and needs more adoption
I just found this comment by chance: https://github.com/capnproto/capnproto/issues/205#issuecomment-148587965
Rusty Russell was considering using protobufs and cap'n'proto for his Lightning Network implementation in 2015.
Discussion
But it doesn't support fixed size byte arrays.
I considered using on a project, but felt it lacks some very important documentation, like what happens when a node tries to communicate directly with another one (instead of routing through many more) and fails? Will it keep trying in the future? Will it not? Is there a limit for retries? Is there a timeout? How can I configure the timeout? Can I disable this behavior? Etc.