I wrote a utf-8 capable (but also fully generic over element type) rope implementation in Rust last fall (edit: 2023) and the main issue I ran into was the lack

I wrote a utf-8 capable (but also fully generic over element type) rope implementation in Rust last fall (edit: 2023) and the main issue I ran into was the lack of a suitable regex library capable of working across slice boundaries. With some finagling I did manage to get it to work with most/all of the other relevant iterator/reader traits IIRC, and it benchmarked fairly well from a practical perspective, though it's not as fast as some of the other explicitly performance-focused implementations out there. I'm afraid I might not have that much free time again for a long time, but maybe when I do, somebody will have solved the regex issue for me...