Vim comes from a time when we did not have screens, you had to print out the code on paper. Probably why it works surprisingly well on mobile. Being able to see the code is a luxury. Typing speed is also not an issue when writing a program, although modern languages are verbose compared to assembly.
I would worry about ergonomics when working on mobile though, like neck/back and thumb issues.
I would suggest having the terminal screen built into glasses, and a wireless keyboard for input. Maybe we can innovate on the keyboard part so it can fit in your pocket