The Old Gods apparently now play a role in Battle for Azeroth. In a quest for the Champions of Azeroth, a servant of the old god N’zoth appears in World of Warcraft.
“He rises!” When you gain reputation with the Champions of Azeroth, you can upgrade your Heart of Azeroth by several item levels with every new reputation level. To do this, you need to complete a quest. At the “Respectful” status, this quest is somewhat longer.
Magni will once again lead you into the Heart Chamber of Azeroth, where you are to empower Azeroth. However, you will be interrupted by a servant of N’zoth, who appears from the void and demands the heart to nourish his master. You repel the servant, and his last words are “He rises!”
N’zoth Revealed
Since the Warbringer video about Azshara, it has been known that the former elven queen Azshara is now the queen of the old god N’zoth. However, the appearance of the Faceless One is the first concrete sign in the game.
There were already signs: Azshara can already be briefly seen in the Shrine of Storms. Her appearance makes it clear early in the game that Azshara will play a role in Battle for Azeroth.
In the area of the shrine and in the open world of Stormsong Valley, there were already further signs. In the instance and around it, there are frequently aberrations that strongly resemble the Faceless Ones, servants of the old gods. Some frescoes on the ground also depict a creature that strongly resembles N’zoth.

Will there be more Old Gods? So far, there are no concrete signs of another Old God. However, there is a fan theory that suggests Yogg-Saron also has a hand in this and that Anduin serves the Old Gods.
Yogg-Saron is apparently not really dead, and he is, after all, the “God of Death.” Even in the pre-event for Legion, players encountered his servants. In Battle for Azeroth, Sylvanas uses chants that sound suspiciously similar and strongly reminiscent of Yogg-Saron.