It would be cool if the easter egg franchises eventually got a full inclusion (The Flintstones, The Jetsons, 2001: A Space Odyssey, Hitchhiker's Guide to the Galaxy) into the game (playable characters, adventure worlds, etc.).
The 2001 level could have a TARDIS pad that takes you to Primal Earth (where early humans observed the Monolith), and the Adventure World could include the new planet, space station, and (probably) some other places. On the space station, HAL could talk to the player (similar to GLaDOS in the Portal Adventure World). Fun Pack with Dave and an Escape Pod.
Hitchhiker's Guide to the Galaxy has several books of content to draw from, and it would be interesting to see the adventure world (it would probably be similar to the mashed-up Doctor Who World). If they have a story level and a level pack level, maybe one could be based off of the movie, and one based on one or several of the books. Level Pack: Arthur Dent, and there are vehicles but I just don't remember any of them right now.
The Jetsons and The Flintstones might work well as a mashed-up world, along with other Hanna-Barbera properties that haven't yet been incorporated. <- Wait, did I just do that? Wow. Anyway, there could be a Jet-stones Team Pack with Wilma and a Rolling Car, and maybe George and the flying car.