Cnohlr did just this, although he strongly suggests using proper interfacing, but having the bare signal wires at hand can be useful for chip to chip communications on the same board. One could build a board with N ESP chips then connect them directly by daisy chaining their TX and RX pins, that is, passing packets in circle, or behind an Ethernet switch chip, de facto creating a board level local network. Might be interesting for some applications.

https://github.com/cnlohr/espthernet