It seems strange to develop a technology that responds to a mental process when, 99% of the time, the mental process (i.e. choice of gear) is governed by a physical process (how fast you're turning the pedals and how much effort - downforce on the pedals - you're applying). A cadence-based automatic gear changer would work just as well in most cases. Leaving your mind free to dream about long, smooth, fast downhills.
Alternatively, and much simpler, you could use a physical process to guide a physical process. Imagine a system where you could select your gear of choice with just a small movement of your fingers. And without needing to carry electronic brain-interpreting software, on the principle that you will already be carrying your brain with you anyway.
Oops, there's me dreaming again...