Versions of PyQt4 compatible with macOS Sierra don't currently exist. PyQtX requires Qt 4.8.2 libs which will not install on Sierra, and PyQtX also fails install. Homebrew no longer offers a compatible PyQt4; it installs PyQt5 which requires Python 3. Python 3 is of course not compatible with FlatCAM.
Unfortunately it seems the only long-lasting, non-duct-taped solution would be porting the project to Python 3.