Ivan,
I am very impressed by your requirement list, it's very extensive! I don't have much to contribute other than maybe my own use-case and experience with publishing photos with OpenACS. I am not a very serious or experienced photographer. I take photos with my Ixus on occasion and what to be able to share them easily with my friends and family on the web. The reason I chose not to use the Photo Album app was that it didn't support bulk publishing which I really wanted since I had about a thousand jpg photos organized into folders that I wanted to be able to publish without too much manual work. To achieve this a wrote a couple of shell and perl scripts to generate thumbnails and mid-size photos and to move photos easily between folders. Then I wrote a simple OpenACS application that lets me browse my photos and directories (I use the glob function to list the photos in each directory). To be able to comment on the photos I also created an ACS object for each photo. This simple setup already does most of what I need. Of course, the EXIF metadata that you mention (in particular the date when the photo was taken) would be a neat addition.
Good luck with the Photo Album application!
