Bethesda's E3 2017 press conference revealed that we'll return to the dingy, dangerous world of Dishonored in September with Dishonored: Death of the Outsider. You can watch the reveal trailer above, showing the return of assassin Billie Lurk and her mentor Daud. Both characters previously featured prominently in the DLC for the original Dishonored.
If you're not familiar with the plot of Dishonored, this tweet basically sums it up.
The Outsider is the source of many characters' power in Dishonored, but his motives are always murky. The lives he touches rarely work out well. Killing him would be quite a feat. Notice that the title doesn't say "Dishonored 2". That suggests this one will be a standalone game of its own rather than more DLC, but we'll have to wait until Bethesda says more to be sure.