So they finally took all of the cool features from F#. What's missing? The pipe operator for railway oriented programming?

Well off the top of my head...

Active patterns, computation expressions, structural typing, statically resolved type parameters, explicit inlining, function composition, structural equality, custom operators and much richer generators.

type providers, units of measure, active patterns, complete type inference.

Not sure I would want the last thing in C#, I think having boundaries at the function signature for that.

Units of measure

F# units are handy, but nothing like Manifold units (Java):

https://github.com/manifold-systems/manifold/tree/master/man...