[Someone]

So, will all of my light bulbs poll that server to see whether they need to execute a state change? Will my doorbell poll the server to check whether it has to ring? Will my fridge poll the server for spot electricity prices and the weather forecast so that it can decide whether to raj the freezer now or in 5 minutes? Will the fire alarm poll the server to check whether one of the heat and smoke detectors triggered?

Some of these will have to poll fairly frequently. For example, users expect lights to go on the moment they flip a switch, not 0.1 seconds later.

Possible? Yes, but taking duty cycle into account, that 5W lightbulb may use more power while switched off than while switched on.

[bryanlarsen]

This problem has been solved for a long time. You can use long polling, websockets, server sent events or some of the older hacks that preceded those mechanisms. Heck, you don't have to use HTTP, you can just use a long lived TCP connection.