Dont even know where to begin here...I have spent my entire career in medical device development (all startups) and the last 15 years in neuromodulation. Everything Elon and his band of engineers and computer scientists and programmers said can be done and isnt anything new or revolutionary. 1000 electrodes is leaps ahead of todays tech (20 or less) but unimaginably short or the Million (billion?) or so connections that would be needed to run major brain systems (no one even knows).
At best this is a medical version of Tesla, massive effort to gather data of a random system (yes, brains are rather randomly wired, like vehicular traffic environments times a billion) to create value by having the largest data set.
Not saying this wouldn't be valuable but in order to control something you must understand how it works.
The first step is to wire up the brain and gather data, on each and every brain. Given the speed of computers today or even 10 years from now this will take a bunch of time, Currently, brains are running 30 times faster than even the fastest computers made and even then that's just number crunching not factoring logic, storage etc
Once each persons brain is mapped then you have to figure out how to write to it, currently we have crude methods of blocking signals with impulses and exert crude forms of "control" over very specific abnormalities. I won't even wade thru the ethics of rewriting brains and the potential for mistakes, abuse etc.
I could go on but HBO's "Silicone Valley" portrayed it nicely...
Here's to a kickass potato cannon...