Over at Arena Nikkei BPnet, they posted some pictures of Sony's booth during CES 2007, which shows a roadmap and plans for the Memory Stick Pro Duo.
click image to enlarge
As you can see if you click on the image, at the very end above 2009, there is a 32 gigabytes of Memory Stick.
There is also a 16GB Pro Duo scheduled for next year. Mind you, all products being shown are ideas and concepts. They may or may not be released. Sony/Sandisk Pro-HG series should be in production this year. The Pro-HG format is a high-density storage option for their Sony devices.