I really like the idea of a proof-of-work captcha, but can it work? The hash requirement needs to be low enough for mobile devices, but scraping and automation

I really like the idea of a proof-of-work captcha, but can it work? The hash requirement needs to be low enough for mobile devices, but scraping and automation are usually done on powerful servers. Is there an equilibrium where it's comfortable for end users, but a real deterrent for servers?