crates.io sees about 13% of requests from nightly compilers, although that may be biased by CI tests that just check for future compatibility rather than needing nightly features.
For application development nightly hasn't been necessary for many years now. Places where people use nightly are increasingly just nice to haves and small optimizations.
https://lib.rs/stats#rustc-usage
For application development nightly hasn't been necessary for many years now. Places where people use nightly are increasingly just nice to haves and small optimizations.