Simulation of code and coding.
I want to validate ideas like test-driven development, mandatory code-review, and required documentation.
Doing this experimentally is prohibitively, almost comically expensive, which is why nobody has ever managed to do so.
So instead I would like to write a simulation that can represent some parameterized assumptions about how developers develop software - how often we introduce defects, how long it takes to fix bugs, etc, with some stochastic variability, and then introduce models for things like TDD and DDD into that simulation.