I'm learning to be IDE-independent and appreciate #POSIX more. After a bunch of hunting for one failing file per each rebuild I came up with a magical solution. The incantation is:

find . -name '*.qml' | xargs sed -i 's/\(import [A-Za-z0-9.]*\)[ ]*[0-9.]*/\1/g'

Which translates to "please remove all versions from import statements in my #Qt QML files"