It's amazing that you propose "just X" to three literally unsolved problems. Where's this micropayment platform? Where's the ID which is uncircumventable and preserves privacy? Where's the perfect anti-cheat?
I suggest you go ahead and make these; you'll make a boatload of money!
They're very hard problems, but still, less hard than blocking AI with CAPTCHAs.
[citation needed]?
After all, Anubis looks to be a successful project to me.
Anubis doesn't block anything. You just have to open the page and wait a few seconds before you can see it. It's just that current crawlers are too dumb to do the proof-of-work, so it blocks them until they can do it.