Myself and some friends need to manage 20,000+ images. Our images grown by about 4,000 per year. We are moving away from folder organization and using IPTC/EXIF/XMP to "organize" our photos.
We use Google Picasa and other tools to search for the photos.
Currently we are using Picasa to create the Keywords and Caption/Description fields for each image.
With 20,000 images this will take a long time. We need a way to batch convert.
Xnveiw has the potential to be the perfect tool to be able to manage this metadata because you already have batch capabilities and some IPTC / Exif functionality. It just needs to be extended and polished.
Specifically, I would like to be able to have XnView run through a directory and subdirectories, grab all JPG's for the first directory, edit (or append) specific IPTC and EXIF data, keep all other IPTC and EXIF data intact, then move on to the next directory.
With each directory, a person could either manually enter in the fields they want to change, our point it to a template batch job file.
The project http://www.exiv2.org/
may help you with many of your Exif and IPTC needs for XnView.
I feel this type of feature will go along way to making XnView more popular. Look at the current state of the web with social bookmarking, tagging, and folksonomy websites. Everyone is tagging their web content with keywords. IPTC.org and Adobe are really pushing with XMP metadata in images.
It will also be important that this functionality can be reached through a GUI. There is already the Exiv2 tool I mentioned as well as the ExifTool Perl Module (http://www.sno.phy.queensu.ca/~phil/exiftool/
). Command line is usable, but not user friendly.
Hopefully Xnview can grow in this area. If not, it's still a great tool.