>None of them have subpixel rendering at the moment AFAIK Actually, most Rust projects end up using Freetype for glyph rendering, which does support subpixel rendering.

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.