Interesting idea, and it was not was not much work to integrate it in Avisynth+, so it will appear in the next release. It will look like
Code:
Subtitle("Roboto Test", x=-1, y=50, font_width=0, font="Dancing Script1002", font_filename="DancingScript-Regular.ttf")
Subtitle("Roboto Test", x=-1, y=75, font_width=0, font="Dancing Script1002")
There was no need to load the font for the second SubTitle.