Vox Media has 46 webdevs and "blogger DNA" which enabled them to build the ultimate CMS for longform:

News organizations across the globe fell in love with the New York Times’ so-called “immersive storytelling” format with the launch of Snow Fall in November 2012, while critics of the project said it wasn’t reproducible or scaleable.  But long before Snow Fall came to fruition, folks at Vox Media — the company that brings us publications like The Verge, SB Nation and Polygon — were already perfecting a system to do similar layouts, reproducibly, with scale, on a deadline.

They don't consider it a CMS. They call it a publishing platform. 

I was asked not to publish any screenshots of the CMS publishing platform, so I’m going to do my best to explain how this works.

Alongside the text editor portion of the system, there are a series of mini-layout options that editors can select. It might be, for example, a mini-layout that includes a huge, full-width photo with a cutline. Or a big right-aligned pullquote. Or a parallax-style background image with a title over it. Or a gallery of multiple photos. Editors can select one of those options, fill in their copy and media, then rearrange those elements within the context of the full story as needed.

“We’re lucky we have an editorial team that’s hands on,” Brundrett said. “That’s what’s important about having the blogger DNA — they don’t already have the abstraction between what they’re making and how it shows up.”

The standard snippet library contains elements that are all responsive, so on mobile they will behave just as elegantly. The snippets provide a framework and standards for the editors, rather than giving them a wide open canvas. For the super complex features that require elements outside the standard mini-layout library, designers and developers can get involved to build out new functionality.

You can see a collection of SB Nation’s longform layouts at sbnation.com/longform. There are nearly 100 on this one site alone, plus another hundred on The Verge’s site and yet more on Polygon’s site.

Readers love this kind of long form and so do advertisers:

“We get really great traffic to these pieces, off the charts engaged time, people are reading all the way down the page, great comments and discussion,” Brundrett said. “From a social perspective they get shared like crazy . They do really well for us.”

Advertisers have also gone nuts over this type of storytelling. Microsoft, for example, wanted to be around the type of work Vox is doing — both in terms of the tech-oriented audience, and to elevate the quality of their brand and show off what modern browsers can do. They’ve sponsored Polygon’s  Human Angle series.