Considering it'll be a sandbox, where every reincarnation has their own goals, ideals and desires, the idea of a unified and cooperative group working together is very unlikely in my eyes.  The more likely scenario is that circumstance and plot-devices will force the players to band together for short periods of time to overcome some kind of larger-than-they-can-handle-on-their-own issue, before breaking up and going their own ways again - or possibly engaging in PvP if their beliefs and ideals are in direct conflict with one another.

At least, that's what I figure. Of course, people might make characters who intentionally share views, values and whatever with one another in order [b][i]to[/i][/b] cooperate and interact.