GS and Mastodon actually seem to have utterly different ideas of what the common format they are working to. They cite different standards, and interpret those standards differently.
The network has adapted over time, and been relatively stable, but Mastodon's growth has broken that assumption.
Now, there's an imbalance, one interpretation of 'standard' is breaking the rest. Yet still people keep up the pretence of a common set of protocols, whilst using them in utterly different ways.
@Rushyo overall I think this is a good thing. Moxie Marlinspike's post about federation comes to my mind about the time when standards block any change and innovation (the time when standards are being adhered to but they are inadequate). I'd rather have a period of flux and incompatibility than feature stagnation and lack of innovation.
Maybe mastodon could say that it rejects the Ostatus thing, and instead declare an external api/interop documentation at this point.