Decentralisation: Their own paper states in 7.2 that "distributed solution will never be as efficient as running the whole training on a local machine". What incentive for buying into this would I have here then? I occasionally use cloud training if what I'm doing exceeds the capability I have locally. As a client I don't particularly care about the internal infrastructure of whoever I pay to do that (with small exceptions like the next point).
Enhanced security: Security that's only required because of me using a blockchain solution? 7.3 starts out with "We assume that the majority of participants is honest.". That's an assumption I can make today with the cloud providers I pay for my training time, without any blockchain overhead. Nothing in that section seems to be related to real world security concerns, e.g. trusting random mining worker nodes with my - potentially proprietary - training data and intermittent results. 3.4, the outline of a task definition, also specifies that I basically provide the full model and really convenient formats to steal all of that away from me. I think the major risk factor of using the idea outlined in the paper doesn't have anything to do with a revolution of cryptocurrencies, but one of the corporate espionage in the ML world it would enable.
Right incentives: For me, as a client, a theoretical 30% savings doesn't outweigh the above (and all the ancillary considerations like infrastructure, ...). If any of their economical analysis is off, they just generate more people going back to bitcoin mining on the other side of the equation. Not sure what the right incentive is supposed to be here. This might be a good system to proove useful work but somehow I don't see the text convincing the reader that the system itself is useful, maybe I missed it.