Can you open calibre in debug mode, try this again, and open a bug report at
https://bugs.launchpad.net/calibre-kobo-driver with all the details?
I will also try the new backend myself
EDIT: I tried the new backend with my Glo and calibre went from detecting to scanning to done in 3 seconds flat. Now, I'm running 64-bit calibre from a RPM package I built myself from source, but that shouldn't make this much of a difference. Perhaps this is yet another Aura-specific bug... looking forward to getting that debug log from you