Assuming you live in a "large" western home, it's impractical. Remember, Edison's first power grid operated at 110/220v DC to the home. If there was lower voltage (IE, 12 volts) going from the street to your walls, the line loss would be significant. It only works in RVs and shacks because the wires are short.

Thus, even if you had DC in the walls, it would be 100+ volts, and you'd still have conversion down to the lower voltages that electronics use. If you look at the comments in this thread from people who work in telco, they talk about how voltage enters equipment at -48V and is then further lowered.