Heh, personally I don't think these kind of top down development style approaches work well with open-source, and collaborative games (SumWars IMHO seems to have failed for other reasons)... I am more of a fan of itterative and interest driven development, e.g. do small steps and let people work on what they want to do.
Besides these kind of design documents would probably change every half year when new people join, while the core gameplay mechanics that would need to be implemented wouldn't really benefit from it.
But since it is fun to speculate about such things (IHMO making such, most of the time overabitious, game design documents is the only thing that come out of many hobbyist projects), we can start making one here.
How about as a back-story we take Alexander the Great's conquest of central asia in order to stray not too far from the 0 A.D. base. The player characters could be new recruits of the wast army, or some tag-alongs looking for fame and fortune, and you could have a diverse style of different enemies, weapons and armors from all the different cultures along the way (they got all the way to the western border of the indian subcontinent). For "magic" we could use some of the (back then amazing) chinese technology like rockets and so on (sorry not a history expert, don't kill me if that was later

), and include different strange animals as companions or steeds.
Basically we should try to use as much as possible from the base of 0 A.D. so that both projects benefit and development will pick up quickly.
As standard character classes there would be obviously the typical fighter... a macedonian army guy? An archer... some (central asian?) hunter tagging along the army to sell his hunt etc.? And a greek philosopher and scientist who travelled to china and came back with a lot of "magic"? Additionally there could be a celtic guy specialized in domesticated animals, or big axes or such

etc. Basically the back-story would fall to the person doing the models for that, just keeping in mind that one should be a close range figher, one a archer and one some sort of specialist with many tricks.
Cooperative game-play mode could be to defend a small scout base against an enemy attack, maybe even with some simple placement of defense structures included, and waves of enemies attacking. Alternatively one could also use the RTS A.I. somehow for controling the enemies. Story driven gameplay (preferrably also possible to play cooperativly) could be the conquest and some sort of scouting missions, or straying from the main army to get some treasures your heard off, or having to desert your soon to be massacered platoon, etc. but that could be implemented much later. Important would be to keep it mission based, and not one monolithic story, so that "outsiders" can contribute missions, and the game becomes playable quickly. Missions should also have replayability in mind, e.g. that is why I find that collaborative against RTS A.I. idea worth persuing.
Ok that's my quick idea, nothing mandatory
Edited by poVoq, 27 July 2012 - 02:23 PM.