We announced that A5 would have it years ago, so even if it doesn't make it into 5.0.0, we should add it at some point. Maybe once there is hardware available for it :)
The standing joke was "mind CONTROL" functionality. (^.^)
Regarding mind reading devices:
I'll have you know devices like these have existed for some time and works. Although their use is experimental, AFAIK there are none available commercially so supporting them wont be an issue for at least another decade or two.
In case it was unclear I was referring to EEG devices designed to learn / recognize certain characteristic electric activity in the brain and use that info to do simple tasks such as controlling an object on the screen. (Like the paddle in the Pong game).
It would probably be a lot more interesting to look at support for touch-interfaces, sensors to detect orientation, acceleration, user motion and eye movement WAY before brain interfacing devices become mainstream. Some of the mentioned technologies have already made it into consumer electronics. If ever considered I'd say implementing the API using 3d vectors would make sense.