BCIs are awesome & there's quite a few companies using hardware, some open source, yet very few reward users for data. 

Thread incoming with some of the 150ish most popular ones.

eth enjoyer working on think2earn and incentives 

Imo tough to predict, guess it's based on how much people are willing to pay for the service (e.g. sleep pattern tracking, or drowsiness detection for drivers). For simpler tasks there are passive methods for collection, like a patch to stick on the forehead, or earphones, but for brain-to-text it can be more complex.

It works well if data is harvested passively. If it requires any kind of chore work what is the chance that would be valued at least minimum wage per hour ?