Saving websites as PDF comes to mind. If taking screenshots of windows as SVG was possible I would definitely use it.
SVG is vector graphics, when you already have pixels - there is no clear way going back.
("Easy" assumed, there is already something there)
(Sorry, I am having flashbacks of the debate with X and wayland, where it was argued, but X is network transparent, except that it wasn't anymore since a long time and, or because - no one used it)
Having features is nice, but not if they are not really necessary and come at the cost of the core feature (performant screen renderer).
If performance was the primary concern, GTK and QT, would not be generations behind (a claim I am skeptical of.)
UI toolkits have a much larger audience than the tiny corner of the industry you work in.