Because it seems as if you don´t know it ratchet:
There are already a lot of games using voxels, as there once was a time at which voxels where very popular for gamedev.
Voxels would allow some great effects. I´ve got no idea on how to do the shading, but that also works somehow. Shadow mapping should work wi†hout a problem for shadows. With raytracing they should allow some even better results than polygons as you´ve got information about the volume of objects.
I think that voxels could really get popular for realtime rendering again.
If you wanted you could probably still use the usual model formats and the importer could make voxelobjects out of it.