There are several interesting observations to be had here. For one, F# already explored (past tense) new language features and has long been essentially feature complete. It gets little features here and there, which are generally quality of life type of things (like anonymous records, for example).
Another interpretation is that F# is just viewed as a .NET/CLR playground and prototype lab to bring features into C#. This is already a common sentiment, but it looks like Microsoft just came out and said it here.
I'll need to read their full strategy, but the blog post is just the same old story: C# is everything, we'll limp along F# with the community doing most of the work, and, oh yea, Visual Basic.
I read through the F# strategy documents, and there's not really anything of substance there. I'm also not sure it's in F#'s best interest to be forced to comply with new C# features (of course F# needs to adopt new .NET features though). F# already does not support several C# features, for good reason, maintaining only what it needs for interoperability purposes. This just furthers the idea that F# is C#'s playtoy.
It's all unfortunate. F# is one of the best designed modern languages around. I wish people would embrace it like Elixir has been embraced. F# could truly be one of the more popular languages and doesn't have to be used at just ".NET shops".