Well Swift for Tensorflow is more than just a binding to begin with. The difference in maintenance is that Google officially supports Swift whereas Microsoft would be always catching up to keep theirs updated.

> So any language that can target .NET is also able to plug into it, and I certainly would pick F# over Swift.

I can use both Swift for my iOS app (inferencing), training is also possible thanks to Python interoperability (@dynamicCallable), soon to be replaced by native C++ interoperability.

If I chose F#, as much as you may think it is a good choice unless your stack/team is using Microsoft technologies, I see this as a potential sunken cost here and I certainly wouldn't use it for this case and would rather rely on the active maintenance of the Swift/Tensorflow team at Google to improve this rather than using another great language for an unsupported use case.