Blight was a slightly divisive league, but not nearly as much as Synthesis or Bestiary, which were consequently not integrated into the core game in the form they were initially released in. After a lot of internal discussion, we have decided to integrate Blight into the core game on PC with the release of 3.9.0. For now, Blight won't be added to Core Path of Exile on console platforms due to some performance problems we need to solve. Our plan is to fix these problems and to integrate it.
Blight will not be present during the main storyline campaign. Once you reach Maps, Blight encounters will spawn in 10% of map areas you enter. Every encounter will drop at least one Oil or Blighted Map. The chance of Blighted Maps dropping has been significantly increased compared to their previous drop rate.
Despite the fact that Blight encounters now guarantee an Oil or Blighted Map drop, Oils are inherently going to be more rare than they were before because you're encountering Blight content less often.
Some feedback from players was that Blight encounters became too easy in very high level areas. Our work on endgame difficulty in Conquerors of the Atlas has certainly affected Blight also, so you should see an appropriate level of difficulty for the rewards granted at high levels.
Once you get a chance to play Conquerors of the Atlas, let us know feedback about Blight's integration and whether there's anything else you feel we should address. Thanks as always!