Why not think about a compact version of the computer without drive?
An optional drive could be still chain-connected on right side. I got this conclusion because the machine has the built-in SD card reader and/or many people also have a real 15x1 drive (or SD2IEC device) so I think the 3.5" drive is not really necessary. It will also help to get price lower.
Anyway, if the floppy reader can be connected as a "sidecar" we can almost reach the original design of the machine.
This option make space for some other accessories, like a keypad connected on right side.
This is a quick mockup I made: http://s30.postimg.org/r48m0ulw1/c65c.jpg