Is there some sort of backward compatibility with the pyuic5 shell command?
I updated to pyQt5 a while ago, but I have a few projects running with pyQt4 on a separate python 3.4 environment. Unfortunately the pyuic4 shell command is now unavailable.
How can I convert .ui files to pyQt4 compatible code?
PyQt5 is not compatibile with PyQt4, hence pyuic5 is also not backward compatible. 
You can install pyqt4-dev-tools package on a debian based system which includes the pyuic4 utility
pyuic5 backward compatibility