One interesting further crossover direction would be to go directly to a USB interface instead of CF/SD. The WCH CH376S lets you mount up a flash drive and address it by LBA sectors (or, more terrifyingly, navigate a FATxx filesystem), over an 8-bit parallel bus. I've seen it used for a few 8-bit micro projects, one of the new-XT-clone projects, and there's a card floating around for an 8-bit ISA interface. Sort of surprised it hasn't become more of a competitor to the CF adaptors, given that low-denomination CF cards are getting scarcer, while 2Gb flash drives are basically more expensive to pay shipping for than to buy.