Running Ethernet without (or close enough to without) PHY was a common trick for 10Gigabit (or more) inside a rack - with Direct-Attach Cables being essentially composed of minimal amount of logic to get two SFP/SFP+/QSFP interfaces on both sides to talk to each other directly.
Thick, ungainly twinax cables, but cheaper than fiber, and 10G-T was latecomer with a lot of teething problems.
Thick, ungainly twinax cables, but cheaper than fiber, and 10G-T was latecomer with a lot of teething problems.