There's nothing stopping you from extending the JSON schema. We'll probably come up with extension points to make it easier (as subobjects, each declaring their own schema IDs).
The format really isn't the interesting question. The interesting question is how do we get clients to behave predictably with each other. If you start breaking the schemas that everyone on the network is using, then yes your posts should fail to render and probably be ignored.
The format really isn't the interesting question. The interesting question is how do we get clients to behave predictably with each other. If you start breaking the schemas that everyone on the network is using, then yes your posts should fail to render and probably be ignored.