The rack module currently allows one device per U. We have clients running two half-width switches mounted side by side in a single 1U using a dual mount kit, and we can't document that accurately, it's either one device in the U or two stacked across separate Us.
Would love the ability to subdivide a U (left/right, ideally configurable widths) so paired half-width devices can each be their own linked asset while sharing the same U row, rendered side by side in the rack diagram.