how to add the ability to bind a hotkey to display the function's arguments? Is it even possible?
You can have company-go insert the arguments for a function when you complete it, like so:
Not quite a hotkey for the function arguments but not too far off. If that is not enough based on https://github.com/nsf/gocode/pull/251 gocode can provide the function arguments for a given function, so showing a popup should not be too hard.