Apple is clearly up to more than they revealed with HomeKit in iOS 8 today. An iPhone can't control your home lights if you're away from home without some sort of connection.
If Apple adds HomeKit support to iCloud, then your phone would have a backend to talk to.
The next step would be getting some device to sit in your house to send the raw messages to all the devices. Maybe this will be built into the next Airports, or could be launched as a separate device. This device would be able to use the iCloud connection.
When you're away from home you could tell your phone to turn off the lights, it would send a message via iCloud which would be picked up by the base station at home.