I think 3rd party services like Prezi, Slideshare, etc. are good for prototyping and/or quick 'n' dirty, ad hoc shows. But for resources that we intend to use over longer periods of time, where we want to ensure consistency and stability, I think using 3rd party services leaves too much out of our control. What if they change the ways they do business? What if they introduce intrusive or inappropriate advertising? Or what if we want to share or distribute resources for use in other Moodles or CMS' or LMS', as in OER, for example?
I think it's nice to be able to zip up a bunch of directories with collated resources that you can upload to your Moodle and display on a course in a couple of minutes.
Plus, some people have problems with setting up authentication to access 3rd party services. And what if a teacher leaves or changes the resources in her/his 3rd party service accounts?
Reveal.js actually does less than the Book resource module but it's quick and slick for slideshows and if it's used with pre-collated presentation packages, it could offer some advantages in terms of ease of use and cross platform portability.
It would allow resource designers and developers to use the authoring tools and IDEs that they're familiar with: create packages on their local machines then send them to Moodle.
It's easy to swap out CSS files to instantly change the styling of the slideshow, which is less prone to the kinds of bad layout designs we see with typical PPT slides: "car boot sale poster" style mixed fonts and text colours, dark text on dark backgrounds, jarring differences from one slide to the next for no apparent reason, etc.
I've tried it with various "exotic" media: HTML video and audio, SVG (inline and external files), animated SMIL SVG, iframes, etc. and it all seems to work well.