We have known going back to October of last year that Google has been aiming for their Aura UI on Linux and the initial target was for version 33, but now it looks like version 35 is when the GTK+ interface will be replaced.
Google's Elliot Glaysher sent out a mailing list post this week encouraging Linux users to install google-chrome-unstable for testing out the new interface.
For why the GTK+ interface is being replaced, there's several reasons. One of the big reasons is that the Aura user-interface is universal across Chrome's supported platforms (sans OS X). The Aura stack runs on Windows, Chromium OS, and Linux so it's easier to ship features for this UI. Additionally, the Aura interface will correct some long-standing performance issues with Chrome/Chromium on Linux, especially with being able to better utilize the GPU on Linux. In particular, the Aura-based Chrome browser will now use one OpenGL context per-window rather than per-tab.
Fortunately, Aura already works on Wayland and should Aura on Linux should be in good shape by the time Chrome 35 ships although additional testing is requested by the Chrome/Chromium Linux community. Those wanting to find more background information on Aura can visit Chromium.org.