Those are for a single serial signal - as the note indicates, mostly to replace very-short-run fiber optics. The challenges with routing DDR4 signals through co

Those are for a single serial signal - as the note indicates, mostly to replace very-short-run fiber optics. The challenges with routing DDR4 signals through connectors, etc are mostly about skew: if any signals are delayed by anything approaching 1/2 a clock period (~1cm on FR4 board) relative to each other, everything is fucked. In addition, some digging on the MAX3800 referenced there indicates that it has a power consumption of 200 mW, and a "budgetary" price of $6.90 each. Since a typical DDR interface is 100+ signals, you're looking at spending 20+ W and the price of a midrange PC just on signal integrity, and that's assuming those chips even do what you want. There are systems that work like Christine - but they are things like IBM mainframes that don't suffer from cost constraints.