(…) (whereas general computing tasks like rendering could be easily verified).
(…)
Rendering is a prime example of something which can't be easily verified. To verify that the miner/worker/whatevertherighttermis actually did the job completely and correctly, you have to check the whole file from front to end. This can't be done by the job author, because they have an interest to lie and keep their GNT, and it obviously can't be done by the worker. Having a third party, or rather multiple third parties check the file is the only option, which…
a) …raises security/privacy concerns, unless homomorphic encryption is used, but in that case, controllers would have to repeat the exact same computation, the worker did(see point c)),
b) …bodes the question why this particular instance should do its job correctly and not just give it a thumbs up, without closer looking, and
c) …eats up a giant portion of potential computing power, because you'd have to check the whole damn thing. This is why there is a reputation system in the first place.
I'm not saying this is not a viable way to go; unlike others, I'm not opposed to the idea of decentralized trust systems. It's just that Elastic is set up in a way which won't need a trust system, at the expense, that some tasks may not be viable (yet).