Tell me about public blockchain apps that do not involve objective money or objective identity, which require strict global consensus, why they should be built on public blockchains, and why haven't they been built yet? I'll consider writing a post, when I get back to it, to explain why it does or doesn't make sense

Here’s two apps that would be best built on public blockchains:

Global education standards and certifications 

Immutable global publishing or media network that anyone can use to access, publish or verify information

Stay Curious // iixii // Lazer Technologies // Prev: CoinDesk, Roc Nation // based

But that's the internet, isn't it? A global publishing network

Yes but blockchains could potentially do it better for information that needs verification, provenance or permanence 

The current internet could be improved especially for parts of the world that are still coming online