[KaVir]

The features you describe have all been implemented in various muds over the years (except perhaps the "probability clouds" thing, but there have been other muds with physics engines and such). So if you're not quite sure how you want a particular feature to work, there will certainly be working examples you can look at and/or read about in detail. The links provided by Ide are definitely a good place to start.

However a mud is more than just the sum of its features. It's essential to have a clear vision at the heart of your design - the glue that holds everything else together.

I used to share that view, ...