Not only you have to hack the routers, once inside the router you'll have to flash a custom wireless firmware, or "radio" firmware. And also the Chipset must be flexible enough to allow all the iFFT shenanigans. I think it's a stretch to say you could do this with a common wifi device, maybe with a very specific wifi chipset you could, and maybe you could make it work with bluetooth or wireless phone chipsets aswell.

That said, it's an excellent paper about a soft-based radar.

IIRC, I think there are some weird FCC rules about external synchronization of radio transmitters. Using the clock would be ok, but synchronizing using out-of-band signals is a problem for some reason. (This is hazy, but I remember working around issues synchronizing UHF (915MHz) RFID readers).