I once put a lot of effort into creating a game such as this. I spent 12 months planning, and with the implementation got as far as having some cool roids and planets spinning on the screen to prove my home built graphics engine actually worked. I then learnt something really important - you have to work damn hard, and smart to create a game.

The other really important thing I learnt was to do with game concept: It is impossible for a team of developers no matter how large to provide enough content for the player base. Instead, a universe has to be implemented that allows the players to unleash their creativity without harming the game. I believe this is the key to a successful on-line universe.

To add some fuel to this argument:
e.g. A set of components and simple smart rules on how they fit together, and a way for players to assemble them. If a player then builds an unbalanced ship, its up to them to mod it till its balanced.... (and to be cannon fodder in the meantime). Capital ships components could then be added to the mix, and its up to the players to assemble one 'correctly' - a bit like a puzzle. If the physics model is as good as I think it is, it should be able to handle ships made of a number of components.

Though the above is a game suggestion, the point I'm trying to make is about a general approach to game design.