I long wanted to see a proof-of-work cryptocurrency that does neural network training instead of burning through hashes. Imagine if 0.5% of the planet's energy consumptions (9 GW) was used for training neural networks instead of mining bitcoin! It would also solve the problem of ASICS being 1000x more efficient than GPUs, so everyone can participate. It would incentivise the development of efficient neural network training hardware. Somebody do this already!