Anybody noticed how closely this, being from the programmer's point of view, is related to what Bret Victor [1] has been talking about from the UI perspective? Take http://worrydream.com/#!/ScrubbingCalculator, or any of the "Kill Math" or "Explorable Xplanations" articles, for an example.

Combining a good UI to the propagators as explained by Sussman in this video, would make a disruptive product on any field where decision making is needed. (Not like such tools didn't exist already in the hands of some, of course.)

[edit] fix typo