I was discussing the game with one of my teammates yesterday evening, and we came to the conclusion that a co-op mode would make a really awesome addition. Although it would be a lot of work to implement, due to the small amount of buttons required, a one-keyboard approach with either split-screen or a single stretching screen could work, no online stuff required.
Co-op would allow for a bit of teamwork, bouncing ships and especially rocks around. Also, it would make it more managable when the RNG spawning system screws you over by spawning multiple huge (!!!) ships on opposite sides :p
Have you guys made any games before this? You seem like you knew what you were doing.