I have already done something similar for an embedded PPC40x board, and I am going to "copy" my previous idea to bootstrap my Zaurus.
I want to support tftboot, a way to transfer files over the ethernet, u-boot uses it to bootstrap devices. Unfortunately, the only available versions of "u-boot" for the PXA chip used in Zaurus don't support the usb frame required to support a usb-ethernet driver for tftpboot. Adding it it would require too much work, so I prefer to modify a Linux kernel for this.
Pretty like in kexecboot, but i don't want to support the LCD and keyboard, my final application will redirect the console to the serial port for everything.
bootlader -> serial console
kernel -> serial console + vterm on screen/keyboard