I've long wanted to run DC in my house, but there's no standard. Do I run 120v, 240v, 5v, 12v? Which interface do I use? Barrel connectors, USB, cigarette lighter? If we have a large-scale movement to household DC, we'd have these things hammered out without me rewiring every appliance.
If these obstacles were overcome, almost everything in my house could run on DC. Most stuff either converts to DC internally, or doesn't care.
Check out the comments to this article. Some say there's one at 24V, some speaking from experience, which sounds sane to me (not an EE but learned these basics and hung out with a lot at college). There's a pointer to a web site in them.
There's not a residential standard, but 48VDC is very standard across the telco & datacenter world. Power over ethernet also runs at 48VDC.