Metabones announced a new 0,64x Speed Booster designed for the GH4. With that new Speed Booster the crop factor becomes almost APS-H (1.28x). And in Cinema 4K video mode the crop factor is almost identical to Super35 (1.5x).
The lens also makes any lens 1.3 stops faster with a maximum possible aperture of f/0.8!!!
There is yet no price or preorder info released by Metabones.