(Replying here since b.p.o doesn't seem to want to let me log in)
I've used the PEP 523 API several times for multiple projects, from analyzing bytecode frequency (which probably could be done with other means) to inspecting type information from function calls. I could probably do such analysis a different way too, (some people do it via tracing). But from what I have experienced, the PEP 523 API is much faster than alternatives, and I would be sad to see it go. I also have written some of these experiments in Rust, and it would make it harder to use if I had to deal with enabling it. I would much prefer the proposed setters/getters.
Best,
Ethan