Thanks pipdo for this update, a few hours ago a new build appeared on connect. Build 5536 which is tagged 'pre-RC1'.
At the moment, only the x86 version is available in English, German & Japanese. Language packs have also been submitted. First reports indicate that both the install and overall performance is better than the previous build.
The screenshots show that the welcome center is updated and the glass appears to be a bit more blue, according to the posts in the forum, flip3D has also been improved.