What is it? A mobile home? No, a house-wide communications and power grid.
It doesn’t exist yet (as far as I’m aware), but it should: a wiring system combining power and communications wires. To reduce interference and improve efficiency, the power supply should be high voltage DC (e.g. 400V). To keep wiring simple and upgradeable, no electronics (hubs or routers) should be needed at sockets or junctions and the number of data wires should be kept low (e.g. 2 or 4).
All electronics should be in the devices plugged in. Because the data wires would be used as a shared bus, several wireless technologies would be relevant, for example contention management and encryption. And because the system could be useful for both large numbers of low-bandwidth devices and a few high-bandwidth devices, it may make sense to divide the data part into two or more sub-systems, allowing usage of old/cheap devices on one sub-system and more frequently upgraded/expensive high-bandwidth devices on another.
Why would it be useful? Well, the same wiring system could be used everywhere in a house, allowing any devices to talk to each other (without worrying about wireless signal strength or extra costs of wireless). Lights could be connected into a communications system, turning themselves on and off at the command given by a switch, mobile or server, with very low extra cost in the light-bulbs. Fire alarms could easily communicate with one another, as could any other sensors you might want around the house (baby monitor, ambient light sensor, security system — you name it).
Assuming high-enough bandwidth communications systems could use the same network (which seems likely, considering the existence of ethernet-over-power devices), the exact same system could be used for home networking — possibly not for video streaming but very likely for internet connections, music streaming and the like. Yay for wired networking without DIY network cables everywhere!
Is that not a system worth asking for? Especially since replacing existing household wiring with DC should increase efficiency (and hopefully finally allow the world to standardise the voltages and outlet sockets so we don’t have to carry adapters every time we travel)?
The other thing which is needed is a standardisation of laptop power bricks, but that’s a slightly different story.