We carry a nanopb integration in Zephyr. And even there... meh. It's true that there are some really bad binary protocols in the embedded world. And protobufs are for sure a step up from a median command parser or whatever. And they have real size advantages vs. JSON for tiny/sub-megabyte devices, which is real.

But even there, I find that really these are very big machines in a historical sense. And text parsing is really not that hard, or that big. The first HTTP server was on a 25MHz 68040!

Just use JSON. Anything else in the modern world needs to be presumed to be premature optimization absent a solid analysis with numbers.