This sort of capability is being introduced into the newest WLAN standards and is being promoted as the next step towards smart homes and devices. The idea being that a standard router can be used to detect human presence, and therefore do things like turn on/off lights, HVAC, etc. This might make even more sense in the commercial space.
This would be as far as I'm aware the first attempt at doing something like this without additional hardware (mounted sensors). It should in theory lower the barrier to entry even further.
There are higher frequency variations of this that could in theory do things like detect breathing. Some people are talking about it being like the new lifeline button or baby monitor.
How well it's implemented will ultimately determine it's usefulness IMO.