Wait, so that was a well known effect when Bret demoed it?!

The idea of using onion skinning to show a bunch successive frames in a game? Yes — it's even a common (albeit naive) technique for doing motion blur.

The idea of moving backward and forward through time to show how small changes lead to different outcomes? Yes — that's why Bret used Tim (the main character from Braid) in his little 2d platformer example.

But the combination of time travel and onion skinning to make a deeper point about abstraction and the general weakness of programming tools (especially outside gamedev)? That's the novelty in Bret's presentation — at least, in my read of it.

But yes game dev has always been way ahead of the curve with making the intangible tangible through visualization. Even things like colouring models based on their internal AI or pathfinding state. This type of thing comes easily because you have a canvas right there to output to, it's actually much easier than print debugging. If every computer program came with a canvas you would see this type of thing for abstract business logic programs as well.