From what I can tell, the concept art is of aliens. As Crowno revealed a while ago, there will be an alien invasion event.
The cultists appear to be worshiping Cthulhu. This could very well be a pre-hardmode event as in Pedguin's live stream, Cenx said that the player was wearing starter-clothing. To me, the player doesn't seem excited, but terrified and trying to escape from the cultists. The event also happens to be taking place at a dungeon. This could be a coincidence, or can only take place at a dungeon. Maybe, a whole new world generation would belong to this event with it an inactive version of the glowing emblem. Even more of a long shot, during the night cultist NPCs could spawn at the altar, and, in a similar fashion to the old man, ask you to summon the boss in some way.
The new mount, visually, appears to have a magnet on the top of it, the blue lasers appear to create sparkles that are being sucked into the mount, and the red lasers destroy blocks. However, it doesn't look like the mount successfully mined stone, as it did not drop when destroyed (from what I could see). The mount will be endgame (also, noted in the livestream) and will "be very op" this item could be obtained in the new lunar event, as one of the sweet drops from later in the event.
Personally, I would love to see kitten armor and Meowmur show up next. Hopefully, it will be adorable.
CONCLUSION: Cenx is awesome. Hands down.
