Ironically, email is becoming increasingly centralized. See this story from just a few days go

https://news.ycombinator.com/item?id=32715437

Yes, as with any protocol email is always subject to centralizing forces. But protocols like email (to me) represent the best possible approach to trying to counteract these forces for Internet applications. They aren’t a silver bullet but maintain the best forms of optionality for undermining and correcting them.

How can they still be in development when the underlying tech has been available for 12 years or so?

In the real world, there is no anonymous e-money that doesn't end up having to be laundered back into good old cash.

Lol yeah so you are talking about a cryptocurrency but actually afraid to use that word. I know, I just did in my other comment and I know I will be attacked here.