Yeah, that's an awesome idea. What if someone started a company like that, that created all of the necessary products? You could call it like, "IntelligentHome." No, wait, "Smarthome."
Maybe there could be a lot of little modules that you could use for home automation, like light switch replacements, outlet replacements, or little plug-in versions of these guys if you don't feel like mucking around in your home's electrical systems. They could all communicate over the power lines in your house. You could control garage doors, thermostats, lights, coffee machines, security systems, irrigation systems, and so on. You could get notifications that the hot water heater is leaking, that there is new mail in your mailbox, that there are rabbits in the garden, that the humidity in your house is too high. When you go on vacation, you could have lights turn on and off to simulate the activities of a resident who is still at home, or feed and water your pets, or cycle the water in some fixtures to ensure your pipes don't freeze.
And because of the extreme simplicity inherent to these devices' interfaces, perhaps you could create a powerline modem and applications that would be able to utilize your standardized powerline communication protocol to, how you say, "control your TV, garage door, thermostat, lights, etc."
In fact, you might even be able to put such an application on your Mac mini media center (let's call this application "Indigo" and your company "Perceptive Automation") and you might even find a helper app for your iPhone/iPod Touch called "Indigo Touch" (for example) that lets you control everything in your house from that device through slick standard interfaces and even gives you the ability to create your own interface (say, an interactive floorplan) to control those devices.