Having looked at it with my very layperson eyes, I struggle to see how it is significantly better than say client side certificates. Same idea - sign a request with local private key, only difference is using the SIN mechanism to let the server know I am to be trusted.
But it's fascinating to see the evolution of these things in real time
TLS supports client certificates perfectly well, and your browser probably supports them.
This scheme also has a lot of beginner-level oversights, IMO. It doesn't delimit the URI from the body, and it doesn't protect the HTTP method itself nor any potentially important headers. This makes me suspect that no cryptographers laid their eyes on this before the announcement.
Client certificates certainly work, but most people wouldn't see them in their browser, let alone seek them out.
I also didn't see if this touched the blockchain at all. They made note about the SIN being public (then again, so is a Public Key), so I'm looking for the SIN to be in a blockchain somewhere.
I discussed it with a govt architect who wanted to get rid of the "bloody database at centre of every application that thinks it needs to store citizens data"
It's a powerful idea