You need a way to anizotrophpic filter the voxels. This means the mipmap should be fully indexable. That is n^3 * m memory for mipmap and n^4 filtering...

Isotopic filtering is easier, just 3*n. However, it will make surfaces look... unreal, as if physics didn't form them, at times.

You cannot wing the quality as easily in 3D though. Continuity is paramount as is some degree of smoothness. Ringing is unacceptable.