[throw868788]

I think this is a problem with many languages - e.g. Scala, Kotlin, etc. The easier justification really is: Does it fit your problem space? Will you save dev time overall, is it more maintainable using this tool? Do your staff prefer working with one tool over the other? Does it meet business objectives?

I don't think F# will ever be more than niche; that I can agree with you. Not because of any technical reason though; perception and marketing unfortunately does matter. Your points around "investment", etc are to me impressions/metrics around that.

In the end these things are just tools. I'm personally in a team that is doing a lot of generic math, and in our .NET based projects F# seems easier and quicker to get that performance. I know C# preview adds some improvements here but it seems more complicated than the F# approach.