Alright, I know this one is kinda a reach, but, aside from adding an entire UI-interactive "app" to build custom SVG filters (inside the Webflow Designer), even adding simple support for the filter: url(…); property inside of Webflow's Designer would be awesome. Right now any custom SVG filters must be applied via Webflow's custom code embeds: SVG <svg><filter id="…"></filter></svg> and/or CSS <style></style>.

If you're unsure of the true power of said expanded filter functionality, I have created merely one example (of effectively unlimited variations) to showcase just this; also linked below...
https://matthewpenkala.github.io/SVG-Filter-Comparison/ 🗗

Also, I'd recommend checking out: https://svgfilters.client.io/ to get a better idea of what I'm talking about.