GIGA G4201TM modems are built for exactly this, using the G.hn standard, over a single pair. I’ve been using these to avoid digging into walls to replace wiring

GIGA G4201TM modems are built for exactly this, using the G.hn standard, over a single pair. I’ve been using these to avoid digging into walls to replace wiring — they claim to sync at up to 1700mbps and, even in the real world, I’m saturating the 1000BASE-T ports.