"We" can't decentralize notifications on iOS, only Apple can. It's not in their interest to do so (battery life, platform brand control via censorship), so it's probably a moot point.
This comes from someone typing this on an iPhone, but that sounds like an argument to drop this goddamn walled garden/prison. I’m literally sick of it.
You also can't use an iPhone without it constantly sending usage information to a half dozen different teams/departments at Apple, even if you've opted out of analytics, so there's that, too. I think I've bought my last iPhone, as well, after having had all of them.
It's better to choose a fight you can win.