Not sure what is the measurable metric here, and what will be considered a success in this trial period.

Propagating the fix downstream depends on the release cycles of all downward vendors. Giving them a heads up will help planning, but I doubt it will significantly impact the patching timeline.

It is highly more likely that companies will get stressed that the public knows they have a vulnerability, while they are still working to fix it. The pressure from these companies will probably shut this policy change down.

Also, will this policy apply also to Google's own products?