And here's exactly such a thing. mLogic have just released a Thunderbolt-equipped PCIe expansion chassis that will allow you to use PCIe expansion cards with your iMac, Mac Mini, Macbook Pro or MacBook air.
These computers now all have the same sort of processing power that was the exclusive domain of desktop computers only a year or so ago, but have always lacked the ability to be expanded with plug-in cards in an external chassis. The reason? Standard I/O ports on a computer are much too slow.
Now mLogic has come up with a practical answer, which may have a profound effect on the way we perceive our laptops in future. For example, Thunderbolt is fast enough to capture uncompressed HD video. It's 20x the speed of USB 2.0 and 12x as fast as FireWire 800. Easily fast enough to use with external plug-in cards.
There's also a special version for the RED ROCKET, which will allow extremely compact 4K workflows for users of RED cameras.