The lowest density chips are still going to be way smaller than even a E1.S board. The only thing you might be able to be cheaper as you’d maybe need fewer SSD controllers, but a 3.5" would have to be, at best, a stack of SSD boards, probably 3, plugged into some interposer board. Allowing for the interposer, maybe you could come up with maybe 120 square centimeter boards, and E1.L drives are about 120 square centimeters anyway. So if you are obsessed with most NAND chips per unit volume, then E1.L form factor is alreay going to be in theory as capable as a hypothetical 3.5" SSD. If you don’t like the overly long E1.L, then in theory E3.L would be more reasonably short with 85% of the board surface area. Of course, all that said I’ve almost never seen anyone go for anything except E1.S, which is more like M.2 sized.
So 3.5" would be more expensive, slower (unless you did a new design), and thermally challenged.
The lowest density chips are still going to be way smaller than even a E1.S board. The only thing you might be able to be cheaper as you’d maybe need fewer SSD controllers, but a 3.5" would have to be, at best, a stack of SSD boards, probably 3, plugged into some interposer board. Allowing for the interposer, maybe you could come up with maybe 120 square centimeter boards, and E1.L drives are about 120 square centimeters anyway. So if you are obsessed with most NAND chips per unit volume, then E1.L form factor is alreay going to be in theory as capable as a hypothetical 3.5" SSD. If you don’t like the overly long E1.L, then in theory E3.L would be more reasonably short with 85% of the board surface area. Of course, all that said I’ve almost never seen anyone go for anything except E1.S, which is more like M.2 sized.
So 3.5" would be more expensive, slower (unless you did a new design), and thermally challenged.