So they're making their own thing rather than using something widely tested and used like Qt?
I find it sad that they felt the need to make their own UI engine vs being able to contribute the changes they feel they need to an existing project. I'm sure Google engineers will tell you that they need to move faster than they could working within the community of GTK or Qt. Plus they don't want Chrome OS to suck because they can't get features merged by the community. They are valid points. The resulting fragmentation just sucks.
I assume Aura is open source. Given GTK's dropping adoption rate and a lot of people unhappy with the recent direction (design or lack of listening to current user base) of Gnome how long until someone writes a general purpose (not specific to Chrome OS) window manager/desktop environment on top of it?
Well, there's CoreOS, though the end result is rather different.
With Qt they will depend on a different company with different interest in mind.
From what I gather, they are switching the Linux builds to use it as well so they don't have to duplicate development effort. I think that makes sense. It sounds like it might be rough and they seem to be aware of it; hence, the urgent call for testers.