Looks like Pentax files a Patent for this lens. Hope it comes true.
http://photorumors.com/2011/01/13/pentax-files-a-patent-for-a-da25-350mm-f3-3-5-6ed-if-sdm-lens/
http://photorumors.com/2011/01/13/pentax-files-a-patent-for-a-da25-350mm-f3-3-5-6ed-if-sdm-lens/