I think Andrew's idea was to connect the RPi's data port to a 4 way or 8 way switch matrix and use the RPi's GPIO buss to switch the switch.
This could be done all with logic chips.
To switch 4 ways would need 2 GPIO lines and 8 way would need 3 GPIO lines.
Using standard GPIO lines as UARTS is possible, but you would need to write the "bit banging" and UART code to be able to do this, something I had to do for my VHDL course I did when doing my MSc.
Kind Regards,
Julian.