This topic has come up a few times on Kurt's Charlie Chan Message Board. I don't remember anyone having specific information about any release dates, but someone did report that the films in question were still being restored, and they would eventually be released on DVD. Perhaps other people who post on both Boards will remember more of the discussion.
sadly, there is no new word on the possible release of the final three Charlie Chan films which are under the control of warner Brothers. The last I heard, they were searching literally the world over to locate suitable copies, and had found none. Most probably that is still the case. I, too, have "viewable copies of the three with "The Red Dragon" being the worst of them visually.
I will surely post any new information should it come my way!