In regards to the plot, the Global Brand Manager at Bandai Namco Games America hinted that the third main installment of the series will be even darker when compared to the first two games. He described that, while there may have been some hope in Dark Souls and Dark Souls 2, that glimmer is gone in the sequel with the world coming to ruin and the bonfires going out.
As for the boss battles, Mike Chang mentioned that there will be less humanoid opponents, when compared to the second title, in the upcoming game. He also added that Hidetaka Miyazaki (the director behind Demon’s Souls, Dark Souls, Bloodborne and Dark Souls 3) brings a certain flavor to the fights. One example that was mentioned was the Dancer of the Frigid Valley, who moves in a graceful manner and can be hard to predict (as it doesn’t telegraph its moves).
Bandai Namco Games will be releasing Dark Souls 3 sometime early next year on the PlayStation 4, Xbox One and PC platforms. If you haven’t done so already, you can preorder the third main Dark Souls installment with this link on Amazon.