Is it better
to store undecoded data streams (like a Catweasel) or
 the decoded data?  My inclination is to deal with raw track data
 without attempting to interpret it.  Requires quite a bit more memory
 to store data, but has fewer limitations. 
 Yeah I guess one way is the "embedded systems" approach and the other
 is a desktop approach. For archival purpose I think your idea is
 better. For daily use (the SVD is a "peripheral" that travels between
 machines) I think the decoded data is probably better. 
 
Ah, we've been here before.
For a "universal disk storage" device or format, you need to have the
capability of three different levels
1) files
2) sectors
3) flux transition
+ software to convert both ways between all three
#3, flux transition ideally calls for the device to have an SA800/SA400
interface, and would not require any additional software on the machine.
Since conversion between USB interface and memory cards is readily
available, either would do.  But, howzbout RS232 and/or "centronics"
parallel?