I love F#, but honestly Microsoft really hadn't built up the kind of trust back then (and maybe even now) to make this an even remotely realistic scenario.
Trust is one issue, another mah be perception. I know Microsoft has been embracing and extending open source recently, but I didn't know F# was open source. Even then, I still have the impression it's very much "Microsoft stack" and not worth investing energy in unless I'm doing "Microsoft stack" stuff.
F# has been open-source since the beginning or at least for a long time (before .NET Core).