There's still a lot of support for 8-bit computers in the fan-groups. The Atari XL spawned Fujinet[1] for networked access which has been ported to a bunch of 8-bits (including the Apple II).
Then there's many (many) implementations of SD-card interfaces to 8-bits, as well as CF cards. You can write to an SD card using the simple SPI protocol, so all you really need is an understanding of FAT32 to create an interoperable transport.