You'd end up with servers welded to the rack.
Then you're not using big enough racks!
More seriously, it's one of the reasons I suggested 600V. I'm surprised you didn't pick up on that part. I wasn't suggesting running 12V through the racks, I was suggesting running 600 VDC. Which, of course, creates it's own issues. Such as a certain amount of theft prevention, but increases turnover in techs.