How about an optional account setting for your location in the form of a zip/postal code, or latitude/longitude, that can then be used to see which other users are located close to you? Not necessarily showing any exact location information, which would be stored privately, but perhaps displayed to other users as something like X miles/km away. Maybe displaying a city at most on the user's page. Which would add something of an
IFPL functionality to FA. I know I'd find this useful just to see who all is near me, and it would of course be an optional thing that people would have to opt into so no one's privacy is in danger.
DA already has something like this, but my main gripe with it is that it only seems to show you a list of who is "near" you, without any indication of how near "near" is for each user. A list sorted by distance would be nice.