Sorry for the confusion - I've been formatting FAT32 since the beginning, using my Mac's Disk Utility. There is some subtle difference between OSX 10.10 and 10.11 that seems to format the USB drive differently, to the point that installation freezes when the USB is formatted from a 10.11 computer. It shows up and mounts properly as sda when I telnet in to OpenWRT and go to /dev (and there's no sda1 or usb in /dev, which is what I was expecting after reading through the support material).
I had the same thought as you, and tried various combinations of v1firmware, v2 firmware, and librarybox 2.1 & 2.0 and always got the same result. It was only when I formatted my USB in FAT32 from an older version of OSX that it started working.
So, great news! Installation is working, and I can log in via wifi to my sparkly new librarybox!
THANK YOU DEVS!!! This is so outrageously cool.
I'm just wondering if there's some way to modify the installation script to account for the changes in OSX 10.11 formatting so that I can do it all from my computer?