I would love this. Absolutely love this. Unfortunately, this is not happening now. The vast majority of 'official'/'governmental' institutions/people seem post on Twitter and, sadly, only on Twitter. Maybe Facebook if you're lucky. I've had to resort to using the premium tier of IFTTT to get things like road closure notices for my area.. it's maddening.
I'd love if they would set up some ActivityPub something under their own domain that I could subscribe to :/
You might have a tiny bit of friction in discoverability but it isn't hard to spread the word when it is about local agencies/administrations.