Slightly slower read/access times to me are acceptable. I'd be more interested in the disk image management on the SD card, preferably through a display on the reader, to drill through to, then select the required disk image.

What are the chances this could expand to a HD20 (or any size disk image) emulator? Of course as disk image size increases, then access time improvements become important again. Ahhh, the vicious circle of development prototyping.