User visible changes in GTK 3.17 / 3.18

Hello,
I've just seen the following blogpost by Matthias Clasen 
https://blogs.gnome.org/mclasen/2015/07/30/1429/

Hopefully it looks good and usefull the same way when looking at his 
screenshots. Because by reading the texts, It appears we will get some 
new and refreshed look and feel not only changing visual appearance but 
also some usability improvements along the way.

This is a part of GNOME that will affect accessibility of almost all 
apps not only GNOME's if it turns out there might be accessibility 
issues related to this new file chooser dialog implementation.

Hopefully this is absolute non sense but with such a drastic change I am 
afraid there really might be accessibility issues.

Has anyone tested this new UI with orca running?
Where can I learn on how to see it in action before it becomes release 
quality?
Is there a testing distribution I can just load in a VM or do I need to 
build on my current GNOME 3.16 install using jhbuild?
What is the easiest way of such quick testing?


Thanks for listening

Greetings

Peter