I too can cast pointers to memcpy'ed C structs. What I can't do in a short order is generate language agnostic descriptors in an IDL that then gets converted to the language of choice to send/recv messages over a wire or file with fast validation. Capnproto does all of this.

So while rkyv looks cool, I think its going to be limited by its language specific tie ins with Rust, and the numbers are skewed towards the unvalidated "deserialization" (pointer casting...).