What you have so far? I question the success of this project. (I'm not flaming you, but just thinking realisticly). If you want to have a 3D-env-where-everything-is-destructable is a hell of a job...
I'll also build my own sandbox where nothing is destructable yet, but that was a hell of a job.

Anyway I'm interested in the technolegies you plan to use. If you go for te dynamic destruction-approache like the destruction of trees in crysis, keep me up-to-date. Maybe I can help help out. I'm not feeling to join the project as I aleady have my own big-huge-3D engine that's still not finished, but maybe we can share stuff/knowlage.

@cronodragon: It can be a lot of fun to destroy stuff in a virtual 3D world as you cannot do in real life.