[praptak]

I am not convinced that flat design implies no visual clues about function.

Granted, the visual clues from bevels, drop shadows and whatnot had the bonus of instant familiarity to people not accustomed to GUIs. Nevertheless this might have been a sort of a crutch and nowadays people even if they expect the computer to emulate their home appliances, the appliances themselves have less and less buttons and levers and more and more touchscreens or at least touch-buttons.