This must have been suggested before, but it's a good idea, isn't it? However, considering how difficult CG found it to change the forfeit button coding, it probably wouldn't be very easy.
I think this would be more useful in situations where you don't want to prompt a scenario where you leave your game to timeout for 3 or 4 minutes; GL Leia is just about to ult and potentially bring back her whole team, for example. Simply doing nothing and leaving the timer to tick away for minutes isn't very intuitive.
I wonder though, whether an 'instant draw' button could lead to offensive advantage scenarios.