That's kind of of the problem, you;re limited by the speed of though when coding. For most things I can type waaaay faster than I can think (a faster keyboard wouldn't help, just as neural output interface wouldn't help much either), and information can be displayed on a computer screen waaay faster than I can read it (so a higher bandwith neural input interface wouldn't help either).
What would truly help would need to be much more complex than that, like something that takes input from something, processes it, then spits the output to other part of the brain, hopefully in a way synced with current visual perception. Or takes input from one part of the brain, processes it through some algorithm, then spits output to another one.
My point is that there's a lot to be gained... but I don't think that trivial implementations of BCIs would bring much gain to highly thinking-limited tasks, so the first generation of them would not be of much use to philosophers, software engineers or mathematicians. Probably the first iterations will help most people fighter/drone-pilots or surgeons, who are truly limited by interfaces-bottlenecks, not thinking bottlenecks.
Though that would soon turn into the mother of all "technical" debt issues...
Imho the future will surprise the shit out of us, despite our ability to anticipate some of the advances... The order shit will happen in will surprise everyone and lead to really unexpected events.
Hopefully we can handle at least some of the things right and steer stuff towards a "successful merge" ( https://medium.com/wordsthatmatter/merge-now-430c6d89d1fe )
So that "miracle" interface would give you, like, what, a 4x increase on 10%, that's like a +4% productivity, in its first iteration, coupled with costs and risks that would make it a really tough sell. We're going to need to go pretty far with the nano stuff to get a good (cost~risk)/(bandwith~latency) out of it. Hopefully there are people working on it and people pouring money into it...
That means for a job that takes 10 + 90 units of time, the 10 section would be done in 2.5, for a total effort of 92.5 instead of 100. That's an improvement of 100/92.5 - 1 = ~8.1% in productivity.