Capacitive coupling Ethernet on backplane
The magnetics serve an important BALUN function to enhance signal integrity of CMRR from crosstalk , mismatch reflections and stray noise from SMPS on ground paths.
At 1Gbps even with spectral compensation training signals for HDMI, even my ASUS tower has problems that are improved with some finger capacitance over the SMD magnetics on high contrast pixel zones with small eye pattern margin. However your backplane design may be better than my HDMI cables. So I use analog VGA for my  1m TV cable to the tower with 200kbps pixel rates or so. Yet my laptop had no issues. Earth Ground is not always “0V” at 1GHz!