Flattr is still running and is used by more than a few major webcomics (presumably other sites as well, I've only really looked at it for webcomics).

Granted it never took off like it wanted to, but Patreon operates on a similar model and is absolutely booming right now. Several comic artists I'm aware of have been able to quit their jobs and go full-time on the strength of Patreon alone--A Ghost Story, for example. So it's definitely not true that micropayment services always fail.

That is not correct. Blendle in the Netherlands is growing in leaps and bounds and has 250000 users who PAY to read good content. https://launch.blendle.com/

Interesting but not surprising that it existed. Reddit gold works because they have hundreds of millions of users and it probably barely pays the bills. Many smarter people have tried tackling the problem, but I don't think drastic online economic changes can grow organically without some sort of catalyst. Maybe if a browser like the one linked in the OP could get enough of a userbase that it becomes a force.