F# has been working well enough on Mac for many years. Even if You won't like Ionide (I hope You will like it ;) ) it's worth checking different projects which allow for F# development on Mac - Xamarin Studio has very good F# support, there are also Vim, Emacs, and Sublime Text 3 plugins / modes for F# (all 3 for core F# language services features are using same backend as Ionide).
Also in context of cross platform development - there exists also F# yeoman generator which provides some nice templates for F# projects outside of VS.
Also in context of cross platform development - there exists also F# yeoman generator which provides some nice templates for F# projects outside of VS.