Will Apple's Greatly Updated Metal Announced today at WWDC Allow Flex FFT Display to Work Better and

Larry, if you think about it, there is incredibly little magic involved that a respectable CPU or GPU can't handle. So, what is 'busy'? 

1) meters - not so much, small real estate.
2) spectrum analyser - not really much happening here either. if you have 1500 or 4000 pixels across your screen all the graphics have to do is literally connect the dots for those 1500 or 4000 data points.
3) waterfall - not too much there, scroll down the view by a single pixel row, then redraw those 1500 or 4000 pixels.

In the cases of 2 and 3 while there are a lot of pixels in the region, the drawing effort is minor as only a small fraction of the pixels there need to be redrawn in the software. 

Or, did you mean displaying the Amateur Radio spectrum on the side of your house?
I suspect the biggest beneficiary to that announcement is 3D games.

Did that cover it or did you mean something different, by way of 'huge breakthrough for supporting Flex?

The FFT data is already being displayed faster than it is arriving. Taken to its ridiculous extreme, you could have 1 pixel represent 1 Hz. Does that really add value? I think sometimes one needs to see aggregate data representation. But, whatever, is that made in China too?