As only webenginepart actually depends on QtWebEngine, with the following patch it is actually possible to build konqueror on systems/arches where QtWebEngine is not supported. The resulting konqueror is then be able to use either khtmlpart or, even better, the KF5-based kwebkitpart currently in KDE git. I have used this patch to keep konqueror current on Cygwin despite our (probably permanent) lack of QtWebEngine: https://raw.githubusercontent.com/cygwinports/konqueror/343027de438903860bdac9a061d0b28ee8242911/17.04-webengine-optional.patch
I think a similar patch is also used by openSUSE, because when installing Konqueror, it works without pulling in QtWebEngine.