You only need one eARC port as you only need one AVR.And tvs only have 1 eARC port so this isn't a good solution even if eARC worked perfectly. Might be something for LG to consider for the X1/11 series next year, add eARC to the other ports.
That's why everyone with more than one console will connect them to the TV. The LG B9, C9 and CX have four 4K120 ports. The LG BX only has two so should be avoided if you plan on having more than one gaming device.So basically to get full HDMI 2.1 functionality for next gen consoles you need to be swapping them in and out constantly, which is not optimal.