Thanks! That helped me get to the bottom of why I couldn't get a screen after reboot. A little too much upgrading. Luckily the first time I tried booting with the later image I was unfrozen.

I'm trying to do this on Windows 8 here, and the network sharing isn't what it used to be, so I'm not sure it'll be possible. I haven't got desperate enough to look into it yet though.

For other people wading through this on Windows, you won't get the Alt_OS partition mounted, so you'll need to mount that from ubiboot's telnet prompt. If you put the Nemo image on your eMMC, you can mount that and untar directly on the phone. I found the best driver for the USB Networking was the same one the Nemo SDK uses, the Acer "USB Ethernet/RNDIS Gadget", though both that and the MS one intermittently cause bluescreens on reconnection, so uninstall them after you're done each time.