Hi ,
Thanks for adding vector graphics support to Paper2D wishlist. I can certainly imagine cache issues you described when dynamically scaling sprites. I’m glad you see some merit in using vector graphics to save storage and perhaps in creating sprites at various resolutions on load.
I looked around for SVG libraries as well and only found Google Code Archive - Long-term storage for Google Code Project Hosting. so far. I also read that WebKit supports importing SVG files and converting to an intermediate format before rasterization, not sure if something like that could be used. NanoSVG library looks really interesting. I’ll keep looking for SVG related stuff.
main reason I like SVG format, is that so many authoring tools support it as an export option or can edit them directly. Exporting SVG files directly into UE4 would save lots of time converting to other pixel based formats, especially if you have to go back and modify original vector graphics at some point, or have to create layers for articulated characters. Anyway, I’m excited about possibilities! 
Wilhelm