Pluggable Rendering Engines?
It is possible to use more than one slide rendering engine, but what would be the advantages of that?
Flexibility is the obvious advantage. It would allow the author to choose their favorite rendering. A particular use case might be an institution that always used impress.js or Flowtime, this would allow a consistent look for slideshows in the wiki.
There should be a generic way of dividing wikitext pages into slides on section boundaries (and failing that, on div boundaries), then each of those "slides" would be rendered as a sequence within the specified engine.