At Photokina Kenko will unveil a variable ND filter. Adjustable from 2.5 - 1000 ND. Note: article in dutch. Source and link: Kenko introduceert variabel ND filter op Photokina - Transcontinenta blog
Well this would be very handy. I'ts quite annoying to stack loads of ND's on top of each other. I hope it is not insanely expensive, so I can buy it for different lenses
