Currently, digikam requires dev-qt/qtwebengine as a dependency (it's listed in COMMON_DEPEND and enabled the ENABLE_QWEBENGINE application flag). Since this package has caused a lot of pain (see bug #669082), would it be possible to turn this dependency to a USE flag? I have modified version 7.1.0 and removed the dependency and have turned ENABLE_QWEBENGINE to off and the application works fine without it. I will do the same with digikam 7.2.0.
No. What this does is use QtWebKit instead, which is much worse and in the process of being removed. If it worked in your case then simply by chance because qtwebkit was already installed.
From upstream build system:
> option(ENABLE_QWEBENGINE "Build digiKam with QWebEngine instead of QWebKit (default=ON)"