Is there any way for a browser plugin to use client-side JS without the site using it? I know this might be a stupid question, but I know very little of extension and frontend development.

That aside, if it isn't too much work to add or support RES features, I would love it and totally use teddit. I (and perhaps some other people here) would even be willing to throw a few bucks your way to help with development/server costs if you open up a donation page.