User blog comment:The Crusader of Truth/The Elder Scrolls Online: Clockwork City Officially Released!/@comment-1600847-20171025113509

I just finished it last night, and the ending teases the next expansion:

"The Triad looms over Summerset!" (the Triad being Nocturnal, Clavicus Vile, and Mephala). Sotha Sil then says the player will need to go there and stop them.

So I guess we're off to the Summerset Isles next year.