Isn't this effectively how MoCA works?
From some preliminary reading it seems like MoCA uses a protocol different from WiFi, since it seems to operate between 1000 and 1500 MHz.
The protocol used is probably more efficient, since it doesn't have WiFi's problem of the signal following multiple paths.
I know this works for normal Wifi modes. Now I wonder if you could get this to work with MIMO. From my limited understanding, it should be possible if the cables have lengths that vary by about 5-15cm.