After a long while of stalled progress, I took my prototype, uploaded it to github, and started to iterate the design with the GNOME Design guys, (aday, lapo, jimmac, hbos...). After a few iterations we came up with something we all were happy with and I moved ahead to create a gtk+ branch. Here is the result so far:
Since I was using Gtk+ 2 for the original preview, I need to figure out how to get things right for 3.0 in terms of layout. However the functionality is pretty much there. I want to discuss a few API problems in the next Gtk+ meeting.
Here's a video of the current behaviour: