C# and Python are my two favorite languages, but what would be cool is using .NET without C#, but using C# without .NET.
The main reason I don't write C# much of the time is because of the .NET dependency. There has always been Mono and nowadays there even is some Microsoft official version of .NET for Linux-based systems if I remember correctly, but really I'd just like C# to be completely independent of an operating system and independent of $someBigCorp.
Using C# without .NET is like using C without libc or POSIX.
There are many standard C library implementations that target various microprocessors and platforms, that enable us to use C instead of assembler. Bringing more high level languages like C# on these platforms would benefit security and development speed.
You could probably strip down .NET core runtime if size is your concern and have an AoT compiled binary that links to that if you're concerned about JIT. I think there was a MS project a while back that compiled .NET IL to static code trough LLVM (https://github.com/dotnet/llilc - it seems dead now unfortunately)
But C# without .NET doesn't really make sense.