Ok, so what do we have to do to build a BCI? First of all, we would want to record brain activity. The one big inventions when it comes to brain activity was the EEG. It is elegant to use an EEG in a BCI, because you do not need to drill a hole in the skull first. You can even produce EEG recording devices that look quite reasonable, or almost so (see picture). The problem with the EEG is that it only gives a very broad impression of what is going on in the brain. Currently, EEG-based BCIs can perform a maximum of 25 operations per minute. This is definitely too slow for flying a plane, driving a car, or even play an ego-shooter on thought-basis.
You would go for the drilling, thus. Modern implantable electrophysiological devices allow to record simultaneously the activity of up to 100 nerve cells in animals (more). Your device would aim at at least 1000 electrodes (more). Currently, you would need a wireless communication system for that, because 1000 electrode devices are still too big for riskfree implantation. But things change... (more)