Australia tried to follow this with gov.au, and it was a bit of a debacle. It ultimately didn't work because it the agency driving it lacked a stick and couldn't coerce agencies to give up their branding/content. Agencies couldn't see the financial incentive -- they'd have to give up their funding and control, and that just wasn't appealing at all.
Frustratingly the idea will be dead for a good time to come now. For an agency to do this, they need a stick -- I believe the GDS had IT spending levers they could pull to control how money was spent across the entire public sector. This made them quite powerful and ultimately allowed them to say "if you want to publish your agency's content, it has to be on our platform".
Not so much “on our platform” (services are surprisingly free in terms of technology and process) but “by our principles”. The GDS assessment process did indeed have clout, in the sense that services could fail, and failure had consequences for funding.
I did two 6-month stints as delivery manager on GDS “exemplar” projects. I remain a fan.
Maybe not platform per se, but through your domain. There's a huge power in that (as gatekeeper of content). It means department's have no choice but to adhere to the standards and recommendations.
The exemplar projects in the Australian system were discontinued after the second round, and were really just lip-service -- at the end of the day, even the exemplar projects were at the mercy of internal Departmental IT operations who ultimately decided what went on to their Departmental domains.
Frustratingly the idea will be dead for a good time to come now. For an agency to do this, they need a stick -- I believe the GDS had IT spending levers they could pull to control how money was spent across the entire public sector. This made them quite powerful and ultimately allowed them to say "if you want to publish your agency's content, it has to be on our platform".
The end result is a far better UX.