By the way for those, who might stumble upon this problem like me, I've solved the problem, it might not be supported and recommended, but this is the solution that worked even on Ignition 8.1.
Only thing missing from the mentioned post are the imports, so here they are:
from com.inductiveautomation.vision.api.designer import VisionDesignerInterface
from com.inductiveautomation.ignition.designer import IgnitionDesigner
from com.inductiveautomation.factorypmi.application.binding.interchange import ExpressionBindingConfig