JSON is just javascript, and it leaves out everything else. That's its entire reason for existing, and it caught on because that's all that 99.44% of anyone needed.
Timestamps you can add today, without changing the protocol; just put them in your data if you need them. So I'm not sure what he's even proposing there.
Schemas: OK, he doesn't like JSON Schema's anyOf. Fair enough. There's no real proposal here for how to fix it, so not much to say here.
Replacing commas with whitespace sounds to me like replacing a very minor irritant with a constant full-body rash. Stuff like his example of "IDs": [ 116 943 234 38793 ] would lead to far more confusion and errors than the occasional stray trailing comma.
So I guess I pretty much vote no on this one thanks for asking