Glenn Watson deserves nearly all the credit here. My role has been limited to a little bit of high-level design input and messing around with signed distance fields and goofy stencil buffer tricks. :)
It could be great for other rust libraries, apps and games. None of them have subpixel rendering at the moment AFAIK and that's super easy with distance fields and real important for appearance.
Signed distance fields are great for animated text, but they also have a couple of disadvantages - they generally produce lower quality output than Freetype at small glyph sizes, and the signed distance field is more complex to generate at start, which slows down initial page rendering. Given that 99% of web pages are static, it's a harder sell. Maybe some sort of heuristic based switching would work.