Original author of smoltcp here! I couldn't have imagined how much of a cornerstone of the Rust ecosystem it would become. Very excited to see it get used like this, and yeah, #![no_std] use cases were the original and primary motivation to build the stack in the first place.
Would something like Smoltcp be of help here? https://github.com/smoltcp-rs/smoltcp
Great project either way!
How do you decide which sys calls to work on? Is is based on what the user space binaries demand?