I wonder if as panel costs goes down, will people start to wire their homes again for 48V DC? You could conceivably run your HVAC and fridges at least off of it, this would negate the need for a larger (more costly) inverter.
The only place it makes sense is personal tech and computing, where USB chargers are cheap and ubiquitous, with technology replacement in 2-5 years instead of 5-10 for standard appliances.
On the usage side for instrumentation, avionics etc. it is usually 28 VDC.
2. Nearly no equipment uses 120VDC by itself, so you would need specialized DC-DC converters that can deal with the 120VDC input to go down to usual voltages like 48VD, 24VDC or 12VDC