I'm announcing the most unpleasant few days of development I've spent.
MultimonitorMode.
It does exactly what it says: it allows you to properly assign multiple wallpapers to two or more screens (depending on whether linux-wallpaperengine supports more than two). And because the dev of binary is goat those wallpapers launch as one process thus why i even bothered to develop this feature in GUI at all.
To activate it, you need to go to the settings.
Unfortunately for some, I don't have a single idea yet on how to nicely integrate this mode with playlists.
I also slightly adjusted the logic and initialization of some components, and replaced some labels with spinboxes near the sliders to eliminate those weird white rectangles with numbers.
This mode also disables individual engine settings for wallpapers, so now you need to adjust Engine Defaults in settings windows since binary that we are calling can't use most of the flags more then twice even if you launch 2 wallpapers in one instance.