The fifth expansion for CE has been announced, and will be available in a few months or so.
Cosmic Dominion is being touted as the "Fan Expansion", because it is largely composed of fan-designed content (aliens, cards, and more). It was also officially designed by three fans: Jefferson Krogh, Bill Martinson, and yours truly. The three of us shepherded the submissions, fine-tuned them, and quibbled vigorously over every detail.
The set will come with 30 aliens (the most of any FFG expansion for CE), and includes a few of the classic Eon aliens that had yet been unpublished in this edition. Some of the classic aliens (like Aristocrat) are largely unchanged, but a few have been re-imagined (most notably some of the remaining lucre aliens).
Having worked on the set, I can say that I am extremely pleased with how it's turned out, and it may be my new favorite expansion. Cosmic Incursion (the first expansion) was the old favorite, mostly because it contained my idea for the Reward Deck. But Cosmic Dominion has its own Reward Deck as well- with some new concepts, and some really amped-up versions of cards found in the original Reward Deck.
Cosmic appeals to a pretty wide range of fans- some like the straight-forward mechanics and effects, and some enjoy the wackier content. Dominion was designed to appeal to the whole spectrum of fan preferences. That said, there will be a few aliens that many fans will just shy away from (something that is probably true of any of the expansions). But I sincerely believe just about every fan of CE will love most of what's in the box.
I'll talk more about specific content soon.