It would be great to have 48VDC in homes, for lightning, light appliances, etc. to centralize the whole power factor control in a single big power supply instead of doing it (poorly, or not at all) at every LED bulb.
The DC power for LED varies based on the bulb and most are less than 48V. Which means you end up with DC-DC converter in each one. DC-DC is slightly more efficient than DC-AC but not enough to make worth converting.
The same is true of electronics, you are replacing AC-DC charger with DC-DC charger.
The other big problem is that lots of appliances require more power than feasible with 48V. People are fine with the low-power DC right up until they need to plug in a space heater. Are you going to have two kinds of outlets everywhere? Or incrementally upgrade each circuit? Or are going to upgrade the wiring with super thick cable that can handle the current?
You would need larger wires to account for the losses at a house scale. Since nothing runs are 48 volts you still have the bad power supply in every LED bulb.
12 gauge wire would work fine for 48v lighting loads; probably 14 gauge too for many of them. Small DC constant-current sources are commodity items now and they're very efficient.
While this sounds great in practice the reality will be far from ideal for the singular reason of security. The cyber issues are compounding at exponential rates as more and more devices that make things "easy" lack even the most basic security protocols and the production targets to generate revenue asap have zero to nil concern around protecting said devices from nefarious actors while in use. When the electrical and data transfer grid become one, as I believe it must for reasons of efficiency, we are certain to witness chaos and losses like never before. What you cannot see matters most! and in time many will pay the ultimate cost for someone else's 'easy'.
More like basically every electronics product uses AC. It’s a two sided market problem - there’s no demand because there’s no supply and no supply because there’s no demand.
The security aspects are solvable through various standards (eg we have LAN over power lines and coax already and they layer encryption on top to build the mesh while balancing UX). The security concerns may be the #1 concern for you but has nothing to do with market adoption.
PoE 802.3bt tops out at 71W. Not even enough to enough to run big USB-C adapter. Also, PoE is pretty lossy which defeats the whole purporse of using DC to save energy.
It'll happen in RV's first, for obvious reasons. I imagine they'll use USB-C as the standard connector even though it's not the optimal form factor for this usage due to its ubiquity. POE would be a better choice.
The same is true of electronics, you are replacing AC-DC charger with DC-DC charger.
The other big problem is that lots of appliances require more power than feasible with 48V. People are fine with the low-power DC right up until they need to plug in a space heater. Are you going to have two kinds of outlets everywhere? Or incrementally upgrade each circuit? Or are going to upgrade the wiring with super thick cable that can handle the current?