I'm thinking that the "box built from junk PC
bits" needs more investigation
 (would make it easy to provide Ethernet support!). It depends what people
 want, though - do they want a box to do data recovery from various floppy
 media (which means a selection of drive types plugged in at once), or do they
 want a backpack-like single drive solution (which implies they want something
 compact, and the bulk of a scrap PC motherboard + PSU is too big)? 
So, NOBODY remembers that these devices WERE commercially available??
In ~1987, there was an aftermarket "external drive for reading PC and CP/M
diskettes" being sold for the Macintosh.  EXACTLY what we're talking
about.  It was a full height 5.25"  case, with a 1/2 height 360K drive.
The remainder of the case held an Ampro Little Board.  And nothing else.
There was a floppy used to "start-up" the "drive", along with software
on
the Mac.  The software on the Mac was, of course, a simple terminal
program.
OB_ reminesce: there two two formats misspelled in their format list.
Both were ones that had previously been misspelled (and later corrected)
on the XenoCopy format list.
I have an Ampro Little Board, but it is in an Ampro case, not disguised as
an "external drive for reading diskettes", and I promised it to somebody
(if/when I dig it out, and remember who I promised it to)
The Quark Megatel (80186?), (or OQO!), might be a better choice for the
guts of the device, due to software availability.
--
Grumpy Ol' Fred                     cisin at 
xenosoft.com