It's entirely possible to design applianced to work from AC or DC.
If the motorized appliances use 3-phase brushless motors, running on DC.. The wall plug could be AC or DC. Any appliances not requiring a 'zero crossing detection' for some kind of timing would be OK as long as it had a bridge rectifier up front, and maybe a PFC for a kind of efficiency that benefits the powr utility. Appliances would have a PFC (power factor correction) front end, which is a switching converter that can run on AC or DC. They usually make about 400V. From this, a motor drive can run directly or a step down DC-DC converter can supply the customary voltages. Things with universal motors (motors with burshes) like vacuum cleaners will work on 110-120VDC, some older variable speed electric drills will not, etc etc. Additionally, houses could be wired with two sets of outlets, 120/240VAC as they are today, plus DC of a common voltage like 150-160V, with a physically different socket of course. Many, many line-operated switching power supplies found in today's electronic stuff (which do not have a big iron transformer up front) will run directly from a 150-160V DC source. This is because the first thing that happens inside things like a PC power supply is the 120VAC is rectified, making 140-165VDC, and this is sent to the witching MOSFET.
Houses with dual wiring could later be converted to all-DC or back to all AC if desired. the wiring size and junction boxes could all be the same only the outlets different.
In the past, some (rural) homes had DC power. Those folks had no trouble with vacuum cleaners or any product with a 'universal motor'. They did have to buy radio sets that were designed for 117VAC/DC. This was in the 1930's to 1950's when the gear had vacuum tubes. You can still find old tabletop radios at swap meets that have this rating on the back. "all american 5" was a generic term, as they typically have 5 tubes, made in the USA, and ran on all USA power.
I had a big old VAX 6000 that ran on 3 phase 208V. Inside I found the first suply, the PFC, made 300VDC. After than, there were several power supply boxes that ran off this and made the +/-5V, etc that the comuter used. It was only necesary to suply single phase 120/240V to the thing, and it ran fine. It could have as easily been run on 300VDC. In fact, in the bottom was space for a huge 300V battery. For scale, the machine was the size of a refrigerator and is what would be called a 'minicomputer'. Just to show, DC is totally practical for use in the home.
