Here's a write-up I made of a talk that Will gave back in 1996, before I went to Maxis to work with him on The Sims. He described his ideas behind "dollhouse" and gave a demo of a very early prototype, so you can see how he not only had the ideas in mind, but also a working prototype, and was willing to show it and share his ideas with a classroom full of students (and a developer who was just sitting in on the class), instead of being afraid somebody would steal his ideas.

Designing User Interfaces to Simulation Games http://www.donhopkins.com/drupal/node/9