To research for a (Pre-)RFC, I want to use Rust 0.11.0 to see what it's like before RFC 241 deref-conversions. The problem is that Rust 0.11.0 is not available via rustup and doesn't support Windows 10 that I'm using, and I don't have easy access to a Windows 7/8 computer (I have a Linux VM, but compatibility is probably another can of worms).
I can't find a Rust playground that supports pre-2015 Rust.
That is 1.11, not 0.11. And in any case that won't help for building it yourself. One version of rustc uses an older version of rustc as bootstrap compiler. If the version you want doesn't support your newer OS version, then an older rustc version won't support said OS version either.
Did you actually try? Windows 10 wasn't released yet when 0.11 was released, so of course it doesn't explicitly list compatibility. Windows 10 should support most older executables just fine though.