Being somewhat paranoid, I want to make sure we get some constraints written down, so that something fundamentally key to something we later want to do doesn't turn out to be impossible.
So, initial list:
Submission method - we're planning to make it web form based, but don't limit it, we can turn this into a pbem engine later, potentially
Processing turns - if we have a mechanism for processing turns as they arrive, it should be easy to adapt to an all at once system if we decide to go that way, so design with on the fly processing in mind.
The engine should allow for the possibility that there can be multiple directly controllable and indirectly controllable units within the players 'party' (for example, villagers within a player's community that can be directed, but might do their own thing, or similar)
There should be a mechanism for GM's to directly alter things, to make things happen within the game world (for example, the GM's should be able to create and then initialise an 'event' that affects the world, players or whatever)
Thoughts, comments, abuse, whatever please ...