I'm not thrilled about your vagueness about what technologies count as a BCI. Little electrodes? The gaming device that came out last year or so got a lot of hype, but the gamers I've talked to who have actually used it were all deeply unimpressed. Voice recognition? Already here in niches, but not really popular.

If you can't think of what interfaces specifically*, then maybe you should phrase your prediction as a negative: 'by 2020, >50% of the smart cellphone market will use a non-gestural non-keyboard based interface' etc.

* and you really should be able to - just 9 years means that any possible tech has to have already been demonstrated in the lab and have a feasible route to commercialization; R&D isn't that fast a process, and neither is being good & cheap enough to take over the global market to the point of 'pervasive'