It looks like in theory it wouldn't be "that hard" to use this to supply Internet access to an old machine like a Duo, albeit in a somewhat roundabout way.
Essentially what the linked dingus does (or can do, anyway) is act basically like an old Hayes smartmodem: it watches the serial input for a special escape sequence to switch it into "command mode". Command mode is used to join a specific wifi network, assign an IP, and to describe what the device is supposed to do while in data mode. (It appears to offer a multitude of options, including sending/receiving raw data over UDP or TCP, encapsulating inside http requests, etc.) The most straightforward way to set this up to provide Internet to an ancient machine would be to set up a simple telnet-like service on a UNIX-ish server providing a PPP/SLIP connection and connect to it using an Internet dialer on the Duo (or whatever), utilizing a custom dialer script to take care of setting up the wifi dongle and underlying TCP connection. (Depending on the level of configuration allowed in the dialer it might be necessary to set the thing up manually using a terminal program prior to launching the PPP/SLIP client. Unfortunately it doesn't use the standard Hayes escape sequence for the command mode, perhaps intentionally to avoid problems with tunneling software that might expect to be connected to a modem.)
So... yeah, not *that* hard in theory but in practice would require a few hours of geeking out to make it work.
