The Red Motion Mount for EF and PL lenses is available now for $3,900. Red explains how it works:
It’s a finely tunable neutral density filter over a wide range of stops. It’s a global shutter that prevents partial illumination with strobes and shearing with fast subjects. It’s a time filter that renders sharper yet smoother pans, artifact-free cyclical motion, more natural motion blur, and reduced or eliminated flicker with lights and electronic displays. Most importantly, all of this can be achieved using a drop-in titanium lens mount that preserves your existing camera and workflow.
The variable ND filter is able to reach 2.4 ND, but with a caveat:
NOTE: In ND Only mode, if the MOTION MOUNT is set near the end of its ND range and used with a very wide aperture you may notice a modified out-of-focus field (bokeh), and possibly some vignetting at the edge of the image with smaller image circle lenses. We recommend that you do not shoot past 4 stops of ND on the mount if you are shooting wide open.
Read more here.