So, suppose it's a rust library -- you're locking me into whatever logging system the library author chooses? Maybe I'd like to consume the relevant data at the entry point and send it to a logging system of my choice.
A Rust library likely wouldn't be returning an opaque Box<dyn Error> to begin with. Errors are part of a library's API—it's what allows consumers to handle them—so you'd define an enum of possible errors your library could produce and return that, which would be stored on the stack.
What about the data in the error payload?
usually “stdout” is good enough, wrapper/runner routes output to logserver for collation and search. who cares about formats as long as it’s reasonably structured and searchable?