The confirmed Reddit leaker (who deleted his 6 year old Reddit account recently, interestingly) months ago detailed that we would see an Adventure compilation, Spelljammer, and Dragonlance products. They didn't mention Spelljammer by name in the UA filled with Spelljammer material, no, but Chris Perkins worked on that UA, and we know that he is working on a Setting book that has Boo the Miniature Giant Spqce Hamster on the cover.
We can have moral certititude that Spelljammer is coming to 5E this year, and this is a very clever metajoke.