Async embedded rust is fantastic. Absolutely nailed it once a couple more unstable features stabilize.

Also on cortex-m, you can put an executor on each cooperative priority but also you can put an executor on the main priority. That means you have one preemptive executor for blocking tasks and a couple cooperative choices.

I should add that I saw a huge reduction in RAM usage going to Embassy from Zephyr for a couple complicated applications. (on the order of 100KiB with all the stack and buffering reductions)