Given the constraints I still haven’t seen an asynchronous proposal for Rust that would do things differently.

Keep in mind that one requirement is being able to create things like Embassy.

https://github.com/embassy-rs/embassy

I agree, I think they should have delayed it.

In a different universe rust still does not have async and in 5 years it might get an ocaml-style effect system.

And in that universe Rust is likely an inconsequential niche language.

If rust skipped async features I think it would not have damaged it much

Almost the entire early large scale adoption came from people writing async web services.

From 2023:

> In that regard, async/await has been phenomenally successful. Many of the most prominent sponsors of the Rust Foundation, especially those who pay developers, depend on async/await to write high performance network services in Rust as one of their primary use cases that justify their funding.

https://without.boats/blog/why-async-rust/