Theoritically you can rip a 3D movie into a side-by-side with dvd quality compression for like 700-800mb. But it 3D PQ and effects will bring tears in your eyes :lol::lol:
It is basically because full HD 3D video requires a lot of space which only the blue-ray can provide. Alternately Blue ray rips are available for (illegal) download, which will be on SBS format, and can be played on any device capable of playing HD files.