Every client wants it. And they actually need it. How do they get it? In a nutshell: active involvement in creating their structured content.
Drupal 7 is bursting with great structured content tools: entities, relations, fields, views, display modes, microdata, metadata, taxonomies and so on.
Drupal 8 plays out concepts behind those tools more fully. (More entities! Better accessibility with WAI-ARIA roles!) And what's more, the tools become easier for content creators to use.
But as is often the case with Drupal, the concepts are eye-wateringly hard to get across. Structured content is just too different from the metaphor of a website as the electronic version of print. (Training that reinforces concepts like pages, chapters and tables of contents is a real disservice.)
Who are the content authors you can share these with? Can they afford not to understand it?
Bring your real-world scenarios of structured content and client training. Let's work out strategies (and indicators of feasibility) for involving client-side content creators as fully as possible in their best options for structured content.