1a graphic engine that shows eyecandies like realtime soft shadows, at least 1.000.000 tris to show per frame (darkplaces has limits in this case)and many more
2a physics engine that uses ragdoll system for a realistic feedback(so no md3 no mdl but a more poweful version of zym, that I think it's possible ro realize)
3a new level engine, maybe integrated with blender, that can create non-orthogonal maps and can "paint" over the the poligons to create dust, blood, and filthness (like painkiller one)
4a cinematic event, or a half-life like script that permits artists to ideate a scene in real time, where actors speak with a morpheme scheme (like half life 2 or better).
5a "story" event, something visual that artists can use to create in game events, like doom3 or better far cry (see sdk on crymod.com for a clarification): I walk in a corridor, and then, a crate fall down and a monster jump up, etc
If programmers really think that this is possible, THAN artists could start to define something. REALLY, I don't want to seem pessimistic, but I think that this is the basis to make something decent. However I'll support every idea for that game mode because I really want to see an Open Source SP game in the net
