I'll be getting a 3k (eventually) and using the Smartmedia as a "permanent" installation with a pen-drive for large capacity USB backup.

I'm don't think multiple slots is going to happen; they cost money. I'd expect enhancements to the USB storage system to be a more flexible solution. Using CompactFlash or xD for solid state storage gives higher capacity "on-board" storage anyhow; there's no point sticking to Smartmedia long-term because development has stopped. Smartmedia has been used so far because it is specifically designed to be a cheap (in terms of hardware cost and software modification cost) replacement for the floppy drive.

Whilst I am on the subject, did we ever reach a definitive conclusion about the compatability (or not) of multi-gigabyte USB devices? Could it be something to do with FAT16 formatting (which is limited to 2 gig capacity) - can the PSR's "read" external devices formatted to FAT32 or not?