Very cool! Font rendering still seems to be a very under appreciated aspect of UI/UX considerations, and with higher-resolution displays rendering performance is definitely more important today than it otherwise has been.

Is the aim to use this in the Xi Editor project? (https://github.com/google/xi-editor for those who haven't heard of it, another Rust-based project of Raph's.)

Not directly. My approach in Xi is to use the system text stack (including font rendering) for a variety of reasons, including consistency of appearance with other text on the system, keeping the front-end small and lightweight, and being able to exploit hardware acceleration to the max.

That said, my hope is that these ideas make their way into at least one system text stack running under Xi. The ideas are simple to implement, and I hope I've made the case that the performance improvement is compelling enough to pursue.