I've followed the instructions on https://wiki.ubuntu.com/Touch/Install, first doing the steps that lead to phablet-flash -b and then the manual ones. In both cases, I get stuck at the Google boot screen. It does not boot into Touch. No errors during manual install, and adb devices shows the device, but I get the following with phablet-flash or phablet-flash -b (second and subsequent times, not the first time):

Device detected as /system/bin/sh: getprop: not found 
Unsupported device, autodetect fails device
When working on flipped images, detection does not work and would require -d

Not clear what that all means.

The Nexus 4 had the initial Touch dev preview on it, FYI. I saw no separate instructions for upgrading from that.