Photoshop CC: Add a keyboard shortcut for brush pressure off and on

Harry, you can do this already at least for size (and opacity).  

 - choose a brush that does not have pressure assigned to size (or opacity)
 - open keyboard shortcuts panel (Windows -> Workspace -> Keyboard Shortcuts and Menus
 - choose "Keyboard Shortcuts" at the top of the dialog
 - choose "Shortcuts For:" as "Tools"
 - scroll down for the choice for "toggle Always use pressure for size (or opacity)"
 - assign a shortcut 

now when you use the shortcut, the checkbox in the tool options bar will toggle.  when it's off, you'll get full-size brush tip, and when it's on, pressure will modulate the brush size (or opacity) from max down to zero.  

let me know if that works for your workflow.