You know, if they were flexible they could do this: For an Alien scenario, you could start as an Egg and go through to a queen. At that point (queen) it would be more strategic based (like Extinction). BUT, you could have the option of switching to a drone (or runner, et cetera) and playing like that, doing quests that the queen cant do. From egg to queen you could do a bunch of quests (i.e. at the start: "Impregnate a Living Host". The main quest could be taking over the planet or, achieving queen-hood (No, that isn't a word).Perhaps throughout the game more hives could be set up, as side quests. For the Marines I think all of your ideas would suffice.
