[neonsunset]

> I'd like everything to be F# with native compilation

This already works today (even with GUI applications) - just define non-unbound-reflection using replacements for printfn (2 LOC) and you're good to go: dotnet publish /p:PublishAot=true

To be clear, in .NET, both JIT runtime and ILC (IL AOT Compiler) drive the same back-end. The compiler itself is called RyuJIT but it really serves all kinds of scenarios today.

> makes F# a poor choice for producing the kinds of precise abstractions needed for an OS

You can do this in F# since it has access to all the same attributes for fine-grained memory layout and marshalling control C# does, but the experience of using C# for this is better (it is also, in general, better than using C). There are a couple areas where F# is less convenient to use than C# - it lacks C#'s lifetime analysis for refs and ref structs and its pattern matching does not work on spans and, again, is problematic with ref structs.