Vacuums and hair dryers invariably use universal motors that run the same on ac or dc. AC motors aren't that common in household appliances because their speed is set by the powerline frequency, which is slow. Typically you find them in microwave oven fans.
They're more common in industrial equipment, but a lot of them there are being converted to run off VFDs, which of course internally run on dc.
But currently every appliance has it's own inverter, so running a fixed voltage add through the house would do little good since every DC appliance wants a different voltage.
All those modern lightweight wall warts are switching DCDC converters anyway—they just have a rectifier and capacitor on the front end to get an approximate DC waveform to start from. That's also why modern power supplies are almost always universal for 240@50Hz or 120@60Hz. The frequency is irrelevant and the DCDC can adapt to a huge range of input voltages because the ratio isn't locked in by the wiring in a transformer.
Modern power electronics are not just more flexible, smaller, and lighter, they're more efficient as well.
