I would like to see the 3.5" floppy do a comeback, for instance as a 1TB+ flash drive. It is large enough that you can comfortably handle it physically and label it, maybe it could be a small throwback to the age of floppies and zip drives.
I love that we can fit tens of GB in a space the size of a fingernail, but it does get rather fiddly to pass around. USB thumbdrives are nice, but are thick enough that they don't really stack up well, or fit into folders and binders nicely.
The 3.5" form factor really is kind of a sweet spot for more than just nostalgia, IMO.