It's all well and good to be able to use IPython notebooks for math and CS related MOOC's, but I think it's a lot harder to translate practical activities from other fields online - I guess interactive features will be the best bet in this regard.
An issue that I can imagine with modelling social security or pensions is that so much can change in the 20-40 years that many users would have until retirement - hence why I (and many others) don't plan based on it!