A 12V bus for the whole data center would certainly be MASSIVE. But within ONE single rack, with separate cables to each blade frame within the rack, it may be practical. If it's borderline, then split the rack in half and do it per half-rack. Otherwise, it would be a SMPSU within each rack frame (this is already done) but that's too small to add a battery to provide the backup power.
A lot of data centers put a UPS in each rack (some as small as 2U but typically 4U to 6U in size) to power the whole rack at an AC line voltage. I don't see why that can't be the point of AC to DC conversion and just supply the DC to each blade frame (usually these are 3U to 6U themselves), eliminating the SMPSU in each frame and having more space for boards.
A lot of this is design issue, such as making blade frames without the SMPSU, and a blade system with just 12VDC.
Apparently a lot of business (maybe Google is among them) are wanting to use cheaper commodity boards instead of manufactured blades. It actually makes business sense, since 4 commodity boards can be put in, in place of 1 blade board.
How this relates to ECN is what the distribution would be within the data center itself. For THAT I really don't see enough advantage (if any at all) to go with DC (whether at 400VDC or 48VDC).
I've seen a few oddball voltages available at a few utilities a couple years ago when I surveyed a lot of their tariffs and installation requirements. I remember seeing 416/240 at two or three of them. One of them even had 240/139 available (apparently a substitute for 240 delta).
I also recall seeing 416/240 as options for pad mount transformers. That is definitely available for dry-type transformers. And it's doable with 3x 240V pole pigs as long as they don't have an internal ground on the center tap (I've been told none have that). A 480/277 meter would handle 416/240. A 480/277 panelboard would handle 416/240. The thing with 416/240 is you have 15% less capacity compared to 480/277 without increasing the amps.
I would not plug my computer into 277. But I would plug it into 240.
If SMPSU makers start making their units work up to 277 nominal, and not just 240, then that becomes a practical alternative. But that would never happen since the domestic voltages in the world are just 100 to 240.
