Digikam doesn't need libgphoto to work. Digikam is an "image management tool" with a feature that allows users to retrieve images from their digital camera. A lot of users don't have a digital camera but use digikam to manage and manipulate their images. There is no reason to intall the (lib)gphoto2 related ebuilds. Other (kde) packages use the (global) useflag gphoto2 for optional gphoto2-support. Would you be so kind to add this to digikam also? Thanks in advance.
The question is not if libgphoto is needed, but if the dependency can be reliably determined. Autodetection leads to wrongly stored dependencies and is a showstopper for a future Portage version with support for proper reverse dependency checking. So as long as there's no configure flag to determine, if Digikam will be built with libgphoto, it won't be optional.
I understand, thanks for the info, I have created a bug-report in KDE-Bugzilla to add a configure flag for this; http://bugs.kde.org/show_bug.cgi?id=118318 If the KDE-bug is resolved I will reopen this bug.
