Dual monitor support is already possible via a single DisplayPort 1.2 connector, but I haven't seen anyone actually implement that part of the spec.

I'm curious to see when the first Thunderbolt GPU will be released. Would be really interesting to see an external GPU attached and driving the internal LCD on a laptop, along with external monitors. Would have really liked that setup back about 13 years ago. I used to have a Gateway Solo 9300 and a single PCI docking station. Inside sat a Voodoo 3, and it would connect to an external monitor. I had one system that I could use at home for gaming, or take it on the road easily, assuming a friend had a spare CRT around.

If you want multiple monitors out of a Mac laptop today, Matrox does offer a dual and triple solution for DisplayPort systems.