I love this stuff. I'd love a heat map superimposed over the code that represents the range of the values and the likelihood or risks of sub expressions overflowing or underflowing.

I'd like to capture the execution flow of a method, visualize it and then watch those visualizations diverge from the old code to the new code.

The runtime could collect a minimal representative set of function invocations and then use that in a visualization during the edit,debug cycle one could see exactly how the new code diverges (kinda like having a column of inputs in a spreadsheet).