Bethesda have posted a teaser on the official Prey twitter in the form of a gif, slowly turning the camera towards the Moon. A speculation storm ensued with many fans praeying for DLC with a strong story component.
Considering this post happened on the same day when Bethesda announced their appearance for the upcoming E3, Prey DLC is all but confirmed as the focus of their presentation during the expo. What else are they going to show, since we know that there is no main Dishonored, Elder Scrolls or Fallout game is scheduled for 2018?
A reddit detective also spotted a certain KasmaCorp account posting low key hints over the last week. Some were responses to Bethesda's employees, that appeared to be random binary code and others were cryptic coordinates. The riddles were solved by SHAPE_IN_THE_GLASS who posted the thread originally while other people pointed out KasmaCorp's twitter account is being followed by several Arkane devs, which led to an assumption these are indeed hints at some new content.
KasmaCorp is TranStar's rival corporation that is looking to get in on the Neuromod market and with the recent activity on Twitter and reddit, it is heavily implied they will be the baddies of the upcoming expansion.
Lack of DLC for an entire year may have been a byproduct of a dreadful release last year when it flopped in sales as well as reviews. The game was riddled with bugs and unlike Arkane's other major project, the Dishonored franchise, Prey didn't take off. It is possible Bethesda kept the project shelved up until now, and it remains to be seen what changed their mind.