Too Long; Didn't Read
Current approaches to layer 2 scaling are moving from theory to practice. Plasma and state channels are not a fully fledged scaling solution for Ethereum. But at the same time, there is a resurgence of a forgotten category of "semi-layer-2" protocols. ZK Rollup promises 500 tx/sec by compressing each transaction to a mere 10 bytes. Shadow chains offer less extreme gains in scaling, but with the benefit of much easier generalization and more favorable security models. The upcoming Istanbul hard fork will reduce the gas cost of data from 68 per byte to 16 per byte, increasing the throughput of these techniques by 4x.