Its not being planned at this time as there is a lot on the programmers list that take priority over this issue. 

Your suggestion is good but I don't think its really the answer because then we could be left with alot of "thumbnail under review" icons that would make the gallery look ,in my opinion, unprofessional. The the image could still be viewed, commented on, etc which wouldn't give much incentive to send an appropriate thumbnail.  The way the holding area works, the images are automatically deleted after so many days of no new thumbnail being sent so its much easier to keep up with it than it would be if they were scattered throughout the main galleries.