It is possible to export the serial TTL console of most routers through Wifi via those cheap ESP8266 serial2wifi modules.
In this example, we use the ESP-12 module powered over a 5V USB cable. As the ESP8266 works in 3.3V, and most openwrt routers works on 3.3V TTL, it is not necessary to do any voltage conversion. You can then connect the GND, TX, RX pins of the ESP8266 to the GND, RX, TX of the router respectively. Alternatively, you could also suck the 3.3V power from on the fourth pin of the serial header, usually labelled VCC.
You can connect to the web interface, unfortunately the console only allows you to view the output of the openwrt console, not to input anything:
However, if you launch programs like "top", you will have a hard time to exit, as CRTL-C does not seem to work.
The goal here is to document how to export serial consoles through the network with the ESP-LINK firmware.