@AG_4AllAges on Instagram (an amazing AG fan who made one of my favorite American Girl movies, Porphyra!) posted this on her story from the new catalog that states that Luciana's Space Suit will be a AG Rewards-member exclusive from January 1 to July 31. Doesn't state which tier, so I assume if you just join AG Rewards for the space suit you can get the space suit. It'll probably release to everyone else around the August holiday release, or on August 1 with the exclusive BeForever bundle (if there is a new BeForever coming in 2018, I haven't heard anything).
This is a pretty smart marketing move, to get people to join AG Rewards.