So far as I know, I am the only clown who has been silly enough to try it on the SI2K. This thread contains my account of this test :-
http://www.dvinfo.net/conf/let-us-di...reme-si2k.html
There is some images of it fitted up to a CP16R film camera here :-
http://www.dvinfo.net/conf/let-us-di...lm-camera.html
I have no intention to make or market any such adaptor. Its up to Le brothers and the other builder-vendors if it is a place they want to go.
The hack for the SI2K is simple enough. All that is required is a P+S universal mount system which is native to the SI2K and the P+S Nikon mount, then a simple adaptor ring for the Extreme which has the grub screws and shoulder on one end and an inner filter threaded shoulder for the front-end of the Nikon lens.
(ADDED TEXT - The adaptor ring would have to made up by a machine shop if you do not have the skills or equipment. It would be no big task. An existing Letus mount ring provides the template for the Letus Side. Your chosen relay lens, Nikon 50mm f1.4, or Nikon 55mm f1.2 or Noct-Nikkor 58mm f1.2 or other brands provides the template for the filter mount thread. On the Nikons it is 52mm diameter and I think 0.7mm thread pitch. You need to have the chosen lens handy so that the machinist can fine tune the thread depth to the lens as there is sometimes some variation according to wear and tear or a slightly flattened edge from being bumped or dropped. Lube the threads when fine tuning the thread depth as the aluminium of the lens thread may gall if the fit is tight and you then have a problem. Stick a piece of thick paper or plastic over the front glass to protect it when going anywhere near machinery with it. )
The Letus Extreme original cine bundle just fits up to the SI2K with the wedgeplate mount set to just enough above the bridgepieces to allow the wedgeplate lever screw to be clear to tighten the wedgeplate.