Yea this is a big gap. It is planned but the task is huge. Once we have sufficient sponsorship or financial support in place you can be assured it will come.
[1]: https://github.com/AccessKit/accesskit I know I haven't yet done much with it this year. Hopefully I'll start doing substantial work on this again in the next few weeks. Threads like this one remind me that the world is waiting.
The main one I’ve been very interested in these days is called Makepad. Also written in Rust, still early in dev, but they need a lot of help on the accessibility front and their codebase is trying to do everything else. But the techniques are what I have been looking for in a UI kit. Anyway, I imagine there are a lot of cases like theirs.
The main issue is most of us do not have these accessibility issues. That domain knowledge needs to be collected and distilled into a framework that is open & simply covers most cases by its inclusion. Many JS frameworks have a lot of care in this regard, but their performance and dep hell make me want to avoid them (however tempting their ease of use may be).
Long story shot: this is very much needed and when I have time I would be willing to contribute.
Rust derive macros would be very powerful with implementing accessibility features.