A level editor would be an easy way for players to add more content to the game by creating it themselves. In summary, the editor would allow you to make something like the current main game where you go through a bunch of enemy encounters and predetermined bosses until you reach the endless onslaught at the end. Players would be able to control how many encounters there are, how far apart they are, and exactly what each enemy would be and how many there are. Players would also be able to make predetermined space hazards (asteroids, comets, and singularities) and decide exactly when they occurred. Perhaps you would also have the ability to post custom messages on the screen to add a story to the level. You could also allow players to decide what music plays and change it at any time. Where bosses are concerned, you could put as many bosses in as you want and decide exactly when they attack, what music played, and it could be any enemy in the game, displaying a large health bar.