The future of CSS layout will be far more complex than what's available to us now. Here's a round-up of layout-related specifications are currently in the works.
- CSS Fragmentation Module Level 3
- CSS Flexible Box Layout Module Level 1
- CSS Multi-column Layout Module
- CSS Shapes Module Level 1
- CSS Box Alignment Module Level 3
- CSS Grid Layout Module Level 1
- CSS Paged Media Module Level 3
- CSS Exclusions Module Level 1
- CSS Template Layout Module
- CSS Intrinsic & Extrinsic Sizing Module Level 3
- CSS Regions Module Level 1
- CSS Positioned Layout Module Level 3
Of these, Positioned Layout, Flexible Box Layout (Flexbox), Multi-column Layout, and Paged Media are the furthest along in terms of browser implementations. Box Alignment and Fragmentation are
auxilliary specs of a sort. They define terms or properties that affect multiple specifications. Box Alignment, for example, heavily affects Flexbox, while Fragmentation is closely related to the Multi-column and Paged Media specifications.
All of this is complicated in the sense that many of these specs overlap and are in flux. That's why I've gathered them here.