The problem with the generators is, that the ...PyImp.cpp is empty when generated with python3. This is only for files that do not exist in the src dir. eg PropertySheetPyImp.cpp in Mod/Spreadsheet/App. There must be anything wrong in the place where these files got generated.
Another idea to support pyside2 without changing the python code:
Place a 'Pyside' dir somewhere at python path eg. usr/lib/freecad/Mod/pymodules. Now wrap pyside2 to the old api. Then the wrapped module should be imported and not the origin pyside module.
There is something wrong with the generators in this branch. Travis reports about generators cannot create files: Traceback (most recent call last): File "/home/travis/build/sasobadovinac/FreeCAD/src/Tools/generate.py", line 29, in <module> import generateTemplates.templateModule File "/home/travis/...