Although I just started looking at slid.es today, from what I've seen I'm guessing that all the building blocks exist already, Either very little or no code is required to export/import manually, maybe only desirable code could be written to automate or guide some steps.

1. Start with a reveal.js (even default) as a template
2. Git push your template site to your Github repo's gh-pages branch.
3. Modify all local URI from local references to remote references.
4. Load all desired assets, eg images into the proper folders.
5. Import the revised template into slid.es
6. Modify however you wish. Note that references to any resources should reference the URI at Github, not the identical file at slid.es. Example: Embedding a picture should not use the slid.es file upload, you need to instead upload the file to your Github repo, then reference that URI in your "Add Picture" slid.es.
7. When complete, export
8. Copy the exported code into the repo on your local machine
9. Git push your changes to Github.

So, here'a suggestion if someone decides to run with this...
It might be useful to support a Profile configuration to switch easily from native (existing) functionality using local or remote URI.

Regarding the Styles that jens noted, I wonder if you can import css into slid.es. That would more or less address the problem (Don't make your original css changes in slid.es, make them elsewhere and import).

Tony

Or if we could download a full version of the slideshow. Now we can only have the slides but styles aren't copied.

And images still refer to the online webpage. It would be nice if there was a possibility to download the whole slideshow and just be able to run it offline. (so you have all files you need)