Very good overview, and it's great that you highlighted the importance of blockchain technology. A few days ago, I wrote an article about how such distributed training systems could be built on top of blockchain, what the incentive system could look like, etc. Take a look if you're interested: https://pub.towardsai.net/blockchain-and-decentralization-paving-the-path-to-true-open-source-ai-1d6929b27785