They could take a tip from those 10-in-1 memory card readers. Somehow, with only two slots, they can fit all the different types of memory card. What I'm getting at is adapters, like microSD inside SD. Build "the hole" for the largest possible (iPod Classic?) and build in adapters for all the others. I can picture a built in solution, with retractable sections depending on the size, but it's hard to describe.