I've worked on a similar approach for Indoor Locationing, I had 5 APs with OpenWRT reading the RSSI of my phone and some Neural Nets implementation, which eventually learned where I am in the house.
this is really interesting, company I work for has recently started working on "location analytics" using signal strength (rssi) of the signal sent when your phone scans for wifi
Video: https://youtu.be/eY0BQJJPdX4