There's a huge opportunity for serialization protocols between PC based hosts and embedded systems. Protocols that are able to serialize without dynamic allocation are really hard to find, so I'll definitely be looking into this.
The dependency on C++ and a rather recent version of GCC is a deal-breaker for some of the embedded platforms I work with, however.
Hmm, I think you'd probably want to treat embedded C/C++ as if it were a different programming language -- so, a separate code generator and runtime library would need to be written. Then you could really make sure everything works in an appropriate way for the platform, without fighting with the desktop/server devs.
But yes, Cap'n Proto would probably be a great fit for that environment, and I'd love to see someone take on this target. :)
The dependency on C++ and a rather recent version of GCC is a deal-breaker for some of the embedded platforms I work with, however.