I had expressed interest in changing it, but it would require changing the core data structure the network is built on, and basically be a breaking change that would almost inevitably result in having to start the entire social web over from scratch. Didn't see huge interest from the devs in doing so.
It sounds like the best path forward might be to document the NodeJS serialization format in perfect detail and create a test suite to verify all known corner cases. Until that's done, alternative implementations will be unreliable.
What are the potential downsides of not changing it?
Makes it difficult to implement the protocol in anything but node.js (and potentially version specific, if node.js ever decides to tweak json serialization stuff)
Objects in JSON are per the spec unordered, while the signature scheme here most likely relies on the order of the object's key-value pairs.
Other data formats that are ordered, and serialize somewhat more deterministically, are CBOR, Protobufs, or s-exp.