Congratulations to Sony for pushing the envelope further in openness. This makes one more device on which it's officially possible to run a pure AOSP system built from source, which obviously makes me very happy.
This is a great example that shows that the tech industry is not a zero-sum game: Sony providing additional capabilities on the Tablet Z didn't come at the expense of any other company, and nobody lost anything in the process. This is pure progress: something that was not possible yesterday is now possible, and nothing was taken away in the process.
I dream of a future where it'll be possible to run a fully Open Source operating system, top to bottom, on any mobile device. I've been working toward that goal for the last 4 years, I'll continue doing so as there's still some work left, and I'm happy to see that Sony is going in the same direction.
As usual, this is my personal opinion.