This isn't actually true -- the latency of Thunderbolt is 1.5 microseconds, which means if you are building something (like a video card) with internal latency expectations, they will all fail.

If it had internal style latency, there would be GOBS of devices pushing to jump on it, but it simply doesn't. You can't even respond correctly to interupts... compared to internal PCI -- it is painfully slow.