I was thinking in using H5P for creating HMTL5 content but I guess it requires Internet access.
H5P would be interesting to make importable. @ivan and @richard have already been looking at how to achieve this from the WordPress / Moodle integrations. But there are no outcomes or roadmaps yet, and it requires that Kolibri reverse engineers the API that H5P has implemented in PHP.
If you want to create simple quizzes on top of uploading contents (videos, PDFs etc), you can design topics and curricula from scratch on Kolibri Studio and export this to Kolibri as channels via http://studio.learningequality.org/
If you want to create rich interactive exercises, you can also use Perseus, which is the renderer that Khan Academy uses and which is already supported in Kolibri. This online editor can create exercises and then serialize them: @storybook/cli - Storybook