You still have to run Romex everywhere, though. People want to run other things in various rooms. They want the option of turning a bedroom into an office should that make sense. That means they're going to see enough power to run a decent sized computer. TV's and bedrooms are common. Stereo systems. Just me and my wife charging our beds by the phone overnight is going to take a significant amount of the power that you allocated to the room.

And again, your whatever voltage, 48 volts, is way too much for an LED, so we still have a power supply. What's the difference between a power supply running on 48 volts DC versus 110 or 220 volts AC? Ultimately, there's not much of a difference, well, you could do a very cheap linear regulator and be horribly wasteful of power, but more likely you're going to be doing a social power supply, which is going to be more complex and have similar efficiency losses. I'm not enough of an electrical engineer to know this for sure but I would suspect the power supply in your Ethernet switch and then the second one to get to that your voltage is less efficient than just having a single power supply that goes from regular line voltage to whatever the LEDs need.