It was speculated in another thread regarding the use of both cameras that the switch likely enables the second camera for 3D purposes only. The question in that thread came up as the phone only uses the top camera when taking 2D shots. It was asked if the second camera could be used instead (perhaps if you get a scratch on the top lens, or the sensor gets some bad pixels...whatever your reason may be).
The notion was that the second camera isn't even enabled until that switch is flipped, so the implication was that the switch has the sole role of turning on the second camera and enabling 3D mode.
That doesn't mean it can't be re-programmed...I think it just means it will take aquite a bit of work, as that switch doesn't perhaps tap into any core part of Android...instead, it may physically enable the second camera and 3D picture mode.
As I move into JB ROMs, I'd like to have another purpose for that switch.