Well, the imagines are about making a flat 4 cyl balanced or not not to reduce cost....a 6 has a similar balancing issue. Common journal or offset much like even or odd firing part of this discussion but with balance not firing. I'm not really sure the definition given in the jalopnik article is a really definition, many V engines (V6s in particular) use offset journal cranks and clearly are not boxers. nor are they as smooth as could be achieved in a flat layout. A flat 6 can be made as smooth as a straight 6, a flat 4 can be made as smooth as a straight 4 with balance shafts....or not if you chose to save money and use a common journal crank. I kind of always assume the name boxer was just describing the way the block looked. I've always referred to them as flat engines but that isn't any better I suppose.
A flat 12 is a bit different animal that does not have any issue that is solved with an offset crank. Each back is already inherently balanced and the 180 angle is already correct for even firing so there is no benefit to any layout other than common journal, and all the flat 12s (inculing ferrari) I've ever seen are common journal designs.
i think this is one of those discussion pointed I'd just end with "OK" because it doesn't seem to need more and since i don't current own any engine it applies to so I have no skin in the game
