The Max scenes are incredibly simple, as are the C4D ones like the test shown above - since they contain no textures or objects of any complexity (so, no third party items, just stuff you can create in seconds in C4D) they are easy to share, don't need any special permissions, and are quite tiny. So, sometime after release we'll make those simple ones available, such as they are :) The will be just a sphere, or sphere and cube, with one volume material applied etc, but you can at least take a look at how they were set up and get to grips with how it all works.
For OpenVDB support, best thing would be to post it in the feature requests section, there's nothing on the roadmap plan for it at the moment.