Any progress on that? @marmistrz: Did you document your approach anywhere, so that someone willing to play with this does not have to start from scratch? Did anyone consider building a Qt5 compatibility layer for Qt4? If you try to port software that doesn't use (m)any of Qt5's new features, it's actually just renaming some classes and reimplementing a few Qml properties. This task is quite similar for many applications and such a layer could save a lot of time if done only once.
fakeroot apt-get build-dep libqt4-dev // add the repo with source or just download the source with debian packaging and cd path/you/need// dpkg-buildpackage -rfakeroot