The next DLC for XCOM 2 has recently been announced by Feral. It is called Alien Hunters and will contain the following according to Feral:

• New gameplay highlighting an elite alien hunting unit of XCOM as it tracks down “Ruler” aliens.
• New mission
• Additional soldier customization options and more powerful weapons and armor

Original-Announcement:

Alien Hunters DLC for XCOM® 2 strikes Mac and Linux soon for Mac for Linux 5 May 2016 The second DLC pack for XCOM 2, Alien Hunters, will be available for Mac and Linux soon. Transform the soldiers of XCOM into an elite alien-hunting squad to face off against new alien Rulers. Using impressive new weapons and armor, these formidable enemies will battle your squad across an entire campaign.