Would also like to have the ability. Same as you, sometimes I use keyboard mostly to interact with browser. And felt the lack of opportunity to toggle VPN. So I need to switch to the mouse to enable it. My guess, it will be a little faster, rather then pressing LMB two times. And also, since the VPN button is rather small, it's a little bit painful for me to aim at it. So it will be better to have a shortcut in this regard too.