I thought express-card adapters are too slow for that hence why both nvidia and ati developed their own standard?!
Edit: "PCIe bandwidth through ExpressCard or an mPCIe connector is not 16x like on desktop PCIe, it is only 1x. This limits the performance of the card to only 60-70% of its full potential if connected by 16x. "
Yes - there is a performance loss, but it can run off 2x PCI-E 1.0 links as well, but still...having a fairly decent graphics card running at 60-70% is still going to be a LOT better than an integrated graphics chip. One of the benchmarks reported a 10x improvement in 3D-mark between the two solutions.
Whilst technically "achievable" - I fail to see the point when you need to have an external PSU, adapter and external graphics card (not to mention monitor).
Could you imagine lugging all that around and having to take *extra* care not to damage expensive kit?
A simple desktop PC would suffice and offer much more flexibility.
I think the point of it is if you have a laptop as a desktop replacement (space requirements etc.) or maybe you take it to work and use it with a monitor at home then it would allow you to play games. The point is that you'd leave the PSU/GFX card at home and only use it when you're at home with your laptop, but you can still take your laptop with you when you're not gaming.