You don't need any big stars if they just don't fit well.Besides the "stars" will require bigger budget and the money they've gave them will make shorter alien and predator action.The only way to make a good movie that includes big stars is to fit them in,pay them and make big action scenes.But you get what the budget must be to make this real.Maybe it's time for Fox to understand that making big movies with big names needs bigger budgets.