See now, I thought of doing the same thing with my netbook (Acer Ferrari One).
What happened is it got delayed. This was through a proprietary XGP port rather than an ExpressCard port, but imo the names keep changing, but in essence both are ports capable of high bandwidth so you don't bottleneck the GPU.
Had a HD4670M, which they called a DynaVivid Graphics Dock. But then the CPU became the bottleneck (its a crappy 1.2GHz thing (dual core) anyway though).
But if this ExpressCard port technology takes off and becomes standard, then this sort of product is going to come in extremely handy, just it might be a pain for some to keep taking their GPU in and out of a PC, or expensive to get a GPU just for a laptop.
Anyway as tech moves on, iGPUs might become better for GPUs, or discrete GPUs might become more common, so laptops are better for gaming. But I found that very often its the CPU which becomes a benchmark, so let's see.
Here, look, almost the same thing, but just nearly two years ago:
Hexus Forum
This technology will be what converts me from a desktop to a laptop. With an SSD and this, performance of a laptop will be almost indistinguishable from a desktop, apart from e-peen benchmarks.
Acer Cheated us a bit because they never but a 5870m in, but a dumbed down 4670, and even then that was only in France, and now its discontinued:
LINK
I mean that was Eyefinity, 3 screens, and HAWX, on a little netbook. Too good to be true in the end because that particular model was never released (as in the XGP thing).
http://www.youtube.com/watch?v=_iqrm_2Gqu8
The way he says "Slim and thin notebook" is funny
He spams that
IMO the same thing will just carry on happening, but it won't ever get into full swing, because by that time, the AMD and Intel APUs will give adequate performance anyway. But the ViDoc is good because you can attach any GPU (I think) into it.