Nvidia, AMD and Apple are all playing with the new high bandwidth Thunderbolt platform, testing its ability to handle external graphics.
One of the big advantages of this new interface is its ability to handle data, power and displayport/PCI Express over one port. This means if you have an external graphics processing units (GPUs) you'd only need a single cable to power it and handle visual signals. In terms of overall bandwidth, Thunderbolt can handle 10 Gbps, making it the fastest standard available today.
While Apple is making some efforts as Fudzilla points out, it seems likely that AMD and Nvidia will beat them to the punch. Considering the standard is an AMD development, chances are that it'll be first to market with something, although Nvidia has developed external graphical products for industry usage in the past, so it too has some experience with this type of graphics usage.
Apparently, the biggest problem that needs to be circumvented at the moment, is that Windows 7 and 8 operating systems won't recognise if the external cards are removed. If you want to do so - without crashing your OS - you'll need to close every application that's using the card.This isn't the end of the world - and this is of course a first step - but it's far from practical.
External GPUs aren't particularly useful for desktop users, but notebook gamers that want a bit of extra power for certain titles would likely appreciate it. Adding an external GPU would also be cheaper and far more powerful than buying a high end gaming laptop.