As much as this approach might be useful for development purposes, I would not recommend that OAuth providers implement an anonymous client id and shared secret for their apps.
OAuth requires the resource owner to understand exactly what is happening at all stages of the process. Removing a vital identifier from this process introduces an unknown element into an already complex process. Therefore this is an anti-pattern in my opinion. I am disappointed that Google have chosen to implement this rather peculiar pattern.
I am aware you alluded to this at the end of the post, but felt the point was worth re-iterating.