This is something I worked on a few years ago when working at Trulia. I was tasked to redesign the homepage. I went with a spilt screen layout with a fixed left panel. As you scroll, the left panel eventually releases, and the layout becomes full screen. I ended up leaving Trulia before this was implemented, but they did eventually implement something in the same vein as this version.
Update: Coded prototype - https://goo.gl/S611hh