Right now, OpenBCI makes products that only handle the "read" side of the equation.
As far as "writing" back into the brain, the coolest thing I've seen was the "BrainNet" project from University of Washington which used transcranial magnetic stimulation (TMS)
The science and tech is advancing very fast, but I think it's not accurate enough to be in everyday use yet as a controller for devices. 90% accuracy sounds great in a paper, but imagine if your mouse clicks or keystrokes didn't register 1 out of 10 times.
What feels way more likely is that we'll see biometric data being collected by more consumer tech devices (cellphones, laptops, headphones) and used as one of many inputs to improve software applications and operating systems. Could EMG or EEG data be used to improve iOS autocorrect and reduce fat finger mistakes? That's a mundane application for crazy tech, but it's the kind of thing that I think will be a necessary intermediate step in us learning how to use these types of signals in everyday ways.
I work at OpenBCI. It's been great getting to work with Gabe and the Valve team. Can't overstate how unique they are as partners on a project like this. Also cool to see OpenBCI (sortof) in the top 10 today :)