I agree! In the new scheme of things I'm not sure how Mono fits into the .NET landscape. I was eagerly waiting to get a answer in Changelog's latest episode[0] but sadly they didn't cover this at all.

It's even more confusing that there is absolutely no mention of .NET Core on the language's Github page - http://fsharp.github.io/

[0] - https://changelog.com/podcast/224