Where has Dan Dixon been developing other software?
And even if he has, consider this: there are several people on the team, like Chris, Georg, etc. They all probably have been working on US3. So even if Dan has taken a little time off for a side project, the rest of the team are still doing awesome things like coding volcanoes or simulating explosions of moons and how their fragments would affect a gas giant, etc.
That's what probably has happened, but first I need explanation on this "project". What exactly do you mean by project?