First post here and just signed up for an account, but I've been aware of SketchFab for a while and love the idea of building a community around model sharing with a nice WebGL viewer - great job!
We've just launched a Kickstarter that essentially is Google Cardboard meets HoloLens offering Mixed Reality at a $30 price-point. It's a combination of some passive physical components (mainly cardboard, but also a wide-angle adapter for the smartphone camera) with some computer vision algorithms. It offers room-scale user tracking, full 3D tracking of two handheld "controllers" for natural interaction, and Mixed Reality support to show models anchored in the real world. We use a video see-through setup rather than the semi-transparent display of hololens, so there is full control of compositing of real and virtual, virtual content will be fully opaque, and it's always possible to render a full VR environment to cover up the camera feed completely (though still benefiting from the room-scale user tracking and controller interactions).
One of the comments from a backer was whether we would include a library of models. We won't have our own library but in my response I did reference that there were 3D model sharing communities such as SketchFab that I was aware of, and that an integration would certainly be technically possible. So the reason I'm here is to see if there's any interest in making such an integration a reality!
Also we're looking to post an update showing more of the 3D model visualisation use case. We've got some of our own in-house models we could use but I think it would make a better story if we used one from the community. If anyone has an animated, roughly human-scale model (doesn't need to actually be a human, but I think a "character" of some form would be best) that they'd like to see in a fully-tracked MR setting then please let me know. We'd let you have approval of the video before posting it, and would credit you fully with a caption and a link back to the model on SketchFab in the text.
One current limitation of ZapBox right now is dynamic lighting so models with baked lighting would be best. We're actively working on adding dynamic lighting but it probably won't be quite ready in time for when we'd want to film this update video.