The need to design such a game is at the confluent of several ideas:
I'm currently pre-thinking the concepts of the game. You can read the current status in the Mission Statements. Of course any contributor welcome (subscribe to the discussion mailing-list), designing the general rules of the game is probably the toughest part of the project.
For the implementation, I'd like to use a higher-level language so that the project is reasonably fast to implement (e.g. 6 months / 1 year) and the program doesn't segfault; since it will probably be quite large and an object conception would map well, I thought of using Ruby. But it's probable that we will need more performance than an interpreted scripting language can offer, so I think we need a compiled language. The problem is that there is very few "usable" higher-level programming languages, so currently my best bet is Objective Caml (with ocaml-SDL, for quick graphics access).