"As the thumbnailer is remote process and thus won't have access to the in-binary resources files, the QQmlImageProvider could perhaps extract them from the binary, provide them to the thumbnailer and delete the temporarily extracted original file again."
As written in comment #3
"As the thumbnailer is remote process and thus won't have access to the in-binary resources files, the QQmlImageProvider could perhaps extract them from the binary, provide them to the thumbnailer and delete the temporarily extracted original file again."