That's pointless work because there's no incentive to do the "mining" (because nobody "wins" ). If you implement a system to choose a "winner" then you didn't need the computations in the first place because you've invented proof of stake.

Why do you need to build the blockchain out of it to begin with? Just use an ordinary blockchain to send payments to people doing inference for you.

Correct: pay for value, not useless hashing.

Exactly