Recently I have been looking at the hardware of certain MP3 players - the so called "S1MP3" players.
These little mp3 players are neat devices - they are based around a Z80-compatible ATJ2085 processor - (http://www.s1mp3.org/files/datasheets/ATJ2085/ATJ2085_datasheet_v1.5.pdf
They are clocked at up to 50 mhz, and can address from 128MB up to 2 Gigabytes of banked RAM, address a small LCD display (some of the MP4 players have 320x200 OLCD screens), a software controlled USB bus interface, a DSP stereo audio output, and so on..
Instead of re-inventing everything with the proposed "Swan" API, which sounds like it is not progressing fast, (no criticism - I have been there..) why not just hack and implement CP/M (maybe +GSX) on these devices? This was the Operating System that used to run on 8080/Z80 CPU's back in the old days - later it became CP/M 86, then DR-DOS, then (currently) OpenDos. There are thousands of Shareware/Freeware/Open source programs for CP/M, and the OS itself is now open software. Being over 20 years old, there are no software patent issues to worry about.
CP/M 2.2 used to run in a few Kilobytes RAM, and it could take care of accessing the basic peripherals - emulated ASCII terminal, FAT (FlashRAM) drives and so on.. Just implement the extra SWAN API features needed as "unimplemented" (in CP/M) INT/CALL routines.
Other observations - a USB keyboard could be connected via the USB port, with some clever hacking to make the USB bus interface act as a master USB device server, operational under CP/M. Or, a spare 5v input line could serve to read a standard (cheap) PC Keyboard serial interface line. If input is via external keyboard, there would be spare output lines - for instance a simple UHF modulator could be driven directly - heck, with a bit of 74xx logic and a UHF modulator (AKA ZX81/Spectrum).
In short, could these very-common-devices serve as a sort of uber-cheap OLPC project for the third world? And would there be any old Z80 coders out there prepared to work on it?