I think this is what is being sought: http://www.villageinstruments.com/tiki-index.php?page=ViDock
, it plugs into the expresscard slot. It has a 16x PCIe card slot, but is electrically only 1x. It also looks like a mining card would cook inside the enclosure.
The Vdock 4 plus is $279+$25 shipping; it would be cheaper to build a mining computer to plug your video card into. Additionally, there are compatiblity issues:"However, only MacBook Pro generations 1, 2, and 4 support graphics cards on the PCIe bus provided in its ExpressCard slot. Other generations of MacBook Pro impose limitations on the memory resources allowed to be assigned to PCIe devices in the ExpressCard slot. PCIe graphics cards used in ViDock require more memory resources than are allowed. Latest MacBook Pro, called Unibody, is generation 5 and unfortunately it is not supported."
The company is looking into a Thunderbold adapter for video cards but has this post on facebook:
"We are still waiting for the Tunderbolt team at intel to release the Thunderbolt developer information / Kit to us. Until they can release it we can not do Thunderbolt development. At IDF they suggested it will become available in Q1 2012. Meanwhile we focus our effort to develop the USB 3 interface for ViDock G4, as such developer information / Kits are available to us. This will in a sense also be beneficial to shorten development of the Thunderbolt version of ViDock G4. We expect the first ViDock G4 to ship in G2 2012. If Thunderbolt will be supported by us at that time completely depends on when intel is releasing Thunderbolt development kit to us and is out of our control."