IIIF is pushed forward by technical specification and community groups. Technical specification groups are responsible for developing new IIIF specifications. Community groups are less formal and can bring together practitioners in a certain domain.
Audio and Video
Active work is underway as part of developing the Presentation v3 specification to add support for time-based media.
You can see more about the work of the A/V Technical Specification group here: http://iiif.io/community/groups/av/
While 3D in IIIF has not been specified there is interst in the community and as of this writing a call has gone out for forming a community group.
There's growing interest in the community on how delivering and annotating IIIF images might apply to various STEM fields.