Recently with the announcement of upcoming seven player support, some concern has been expressed over the increased frequency of Cosmic Quakes. In the spirit of reassurance, I would like to remind everyone of the potential to include Antibodies in a future expansion. For those unfamiliar, Antibodies are a special encounter card coded to a specific colour. Each has a main value, and a secondary value if played by or against the alien of the appropriate colour. This facilitates deck expansion nicely, as you only include the Antibodies corresponding to the colours in play - more players means a larger cosmic deck.
Of course this does mean the main deck gets significantly bigger even in four or five player games. One thing I like about the reward deck is that it tends to delay Cosmic Quakes in practice (players are bound to want reward cards at least some of the time), while in theory a Quake can still be engineered by actively avoiding the reward deck.
Regardless, I think Antibodies would be fantastic in the cosmic deck. I also like that they add both Attacks and Negotiates. They should probably come in the last expansion (at least the last which adds a player) so that future sets don't need to include new Antibodies