Well the Sansa View came out a short time ago, and good news: it's PortalPlayer based (Nvidia)! And it looks to use the same basic firmware/bootloader (rom+mi4) layout as the c200/e200.
Use the latest version of mi4code to decrypt it with the key:
70e19bda 0c69ea7d 2b8b1ad1 e9767ced (v 1.00.03)
(found via mi4code keyscan on BootLoader.rom)
Firmware is available for download from:http://forums.sandisk.com/sansa/board/message?board.id=view&thread.id=326
Decryption works just fine, and there is a classic PPOS header in when the firmware is decoded. There appears to be a reference to the NVIDIA GoForce 6100 http://www.nvidia.com/page/goforce_6100.html
, which features, among other things, a "Dedicated high performance 250MHz ARM1176JZ-S core"
Looks to be very close to the Sansa e200/c200 series in terms of the bootloader/firmware sections. So I would assume a properly made binary could be signed with the above key and executed on the player.
Player can be put in UMS/MSC mode via a startup hack:
Let it boot up up, put the hold switch on. Hold down the left side of the scroll wheel and plug the usb cable in at the same time. Keep holding it until a drive appears. Can someone do an fdisk -l output?
Now, if someone with a View using 1.00.03 firmware could trying the decrypt/encrypt the firmware and see if it runs...