One thing that I've always wondered though: with the 18650 cell being cylindrical, won't there be wasted space between them in the pack? Wouldn't it be better to design rectangular-shaped cells, so that they are stacked more efficiently in the pack?
Packing circles is approximately 91% space-efficient. I figure the weight and cost are far more important than a tiny amount of space.
Yeah, 90.69% to be exact. I guess, like you say, other factors are more important than 10% higher energy density.