Chips that can’t fit on a 76mm board do not exist in any market. There’s been some fringe chasing of waferscale for compute, but it’s a nightmare of cost and yield with zero applicable benefits for storage. You can fit more chips on a bigger board with fewer controllers, but a 3.5" form factor wouldn’t have any more usable board surface area than an E1.L design, and not much more than an E3.L. There’s enough height in the thickest 3.5" to combine 3 boards, but that middle board at least would be absolutely starved for airflow, unless you changed specifications around expected airflow for 3.5" devices and made it ventilated.