At Olo, which is primarily a C# shop, people have been excited to learn F#, and able to pick it up on an as needed basis. We are pretty large and it has been fine. It helps quite a bit that it is a different language but part of the same ecosystem. It is quite a bit easier to manage than it would be adding say, Go, or Rust or something into the company, with entirely new tooling and libraries. for instance a visual studio solution can contain C# and F# projects, and they can refer to each other.