Some comments here express some head scratching on what exactly Sway is. I only saw the demo video like everyone else so I don't claim to know definitively but here's my take on where Sway fits.
It looks like we're in a general upward trend of richer interactive documents created by average users.
Some observations of the zeitgiest that look unrelated on the surface but nevertheless, seems to point towards a common desire for dynamic user-controlled "documents":
-- Javascript d3.js embedded in stories, blog articles, etc that engages readers to "play" with data (Mike Bostock is a good example of interactive pictures for New York Times) [1],[2]
-- Mathematica CDF (Computable Document Format) with things like sliders, etc to let the user control how the data changes[3]
-- Bret Victor's various demonstrations for dynamic content [4]
-- many more examples, etc. I cant remember but play on this theme
Right now, there isn't an interactive document format (or interactive content creation tool) that dominates the way Microsoft PowerPoint dominates for the old-style static stuff.
If one has the skills, one can write d3.js type presentations but obviously, the typical PowerPoint jock isn't not going to learn javascript like Mike Bostock.
Before d3.js, if I personally wanted to write any interactive charts for presentation and embed that interactivity inside a document that managers could review offline, I'd create an Excel spreadsheet + add some GUI slider controls + add some Visual Basic code to react to sliders to update the spreadsheet.[5] Unfortunately, any xls (xlsm) file with a macro throws up all sorts of scary security warnings when a user open the xls file. It's just very clunky to share this type of doc.
It's hard to tell from the demo, but it seems like Sway is also a tool to author content intended for non-linear exploration. (Whereas PowerPoint or MS Word docs are consumed in linear fashion ... PgDn, Pgdn, etc). Therefore, some of its features would overlap with an eLearning-creation tool like Adobe Captivate[6].
In short, I believe the market is trying to sort out how to empower averager users to make dynamic presentation content. The d3.js, the Excel macros, the Mathematica CDF, etc are tools that are too specialized and meant for experts. This is why the demo commercial emphasized a young child creating materials instead of an adult programming expert. It's the "so easy a child could do it" type of narrative.
I can't tell from the demo if the content created would be 100% cloud stored and delivered. I would think that Sway would also have the capability to create self-contained document files. I can think of big customer like the USA government not using it if it's cloud only. The government loves their Powerpoint presentations. The government also has tons of locked down computers without internet access that share Powerpoints so a 100% cloud-Sway product would be a no-go.
EDIT ADD: after looking at sway website again, I finally noticed that they have 6 example Sway presentations ("Sways we love"). None of those examples have any interactive data features that I could detect. On the other hand, the video @ 34 secs shows the woman manipulating a chart. The 6 example docs are not that impressive; they just look like a bunch of jquery sliding animations instead of representing the dynamics I see in the video. Maybe I'm overestimating what Sway actually can do. If it's just a program with a bunch of themes for sliding animations and adjustable grids that resize to desktop or mobile screens, that would be a huge disappointment.
[1]http://bost.ocks.org/mike/
[2]https://github.com/mbostock/d3/wiki/Gallery
[3]http://reference.wolfram.com/language/howto/CreateAComputabl...
[4]http://worrydream.com/#!/MediaForThinkingTheUnthinkable
[5]http://chandoo.org/wp/2013/08/06/how-to-create-a-then-vs-now...
[6]http://www.adobe.com/products/captivate.html