Less is more, a timeless trend. Where simplicity means cleanness, for a white-dominated, neat page in the name of minimalism. The space is the king: its optimization works for a multi-functional, versatile design.
Adding some sauce at traditional flat design might be the right direction for 2018: a little bit of shadowing will help to give objects a more round dimension, while the minimal attitude that made flat a big thing is still dominant. Spaces and depths will find their dimension, literally, within these extra-deep concepts.