> I'm a little suprised to learn there's no self-reference support in protobuf, as I wouldn't have assumed parsing that would be an issue (as all it really is is a pointer to an existing object in the message to say, put a ref. to it here), though I guess it might be a problem in supporting certain languages.

That's a tradeoff more designs should have, IMO: reduce the feature set as much as possible, but in return make the implementation vastly simpler. :)

I assume it's not only about support in programming languages, but also exactly to eliminate the entire class of bugs that stems from back/forward-references in serialized data, and to generally keep the wire format as simple (to parse and to implement a parser for) as possible. The few usecases that could make use of references are not worth the pain inflicted on everyone if they were implemented.