I am not entirely sure I could code at 240 words per minute, even if my brain were directly connected to my computer via a thought to text engine, unless it could translate visual thought concepts.
But that would be in the realm of sci-fi, where you could create a UI and make it work, by just imagining yourself using it.
Currently, I'd have to say the bulk of my development time is not spent on actual typing of code, but rather testing, debugging, and research, and I don't see learning stenotype shortening the time spent doing that, by very much, even at double that rate (480 WPM).