This, or variations of what you describe, is clearly the right path for instant presence detection. I saw hints in hub v2 threads that it’s being looked at. But why wait since most of our phones already support BLE. Would be awesome if this was built into the app so we didn’t have to do 3rd party apps and hacks. There is already a variety of battery powered BLE beacons available or launching soon.
The v2 Hub integration potential is also exciting. Would like to have the battery powered BLE beacons in my car and backpack etc and have hub know when I or other family members arrive. And tie in with phone app integration as you suggest, and my phone could tell the hub which room was occupied if I put beacons in each room. Can’t wait until this gets mainstream. Won’t be long now.