F# is an interesting language in lots of places, but it's still not an all-purpose .NET language. You won't get design/tooling support for WPF, ASP.NET, or Blazor. (Yes, I know there are third party projects that add some of this, but these layers have costs.) So I don't F# can fill the VB niche because it doesn't make sense either as a programmer's "only .NET language" or as a learning language for novices.