Honestly, I think the best argument (and the only one I buy) for Swift is the latter part: “…we were more familiar with its internal implementation details - which allowed us to implement a prototype much faster.” – just like I said about a year ago [1]. If you are sitting on a team deeply familiar and passionate about a language – Swift – what kind of managerial fool would not let them take a stab at it? Especially with Lattner’s excellent track record.
[1]: https://news.ycombinator.com/item?id=16939525
The ideas behind Zygote dates to somewhere around spring 2017, but I think it took about a year to hammer out compiler internals and find time to hack, so you are still right that nothing was public when Google settled on Swift – I think there been at least one Mountain View visit though over XLA.jl, but do not quote me on that one.
The race is still on and I am looking forward to seeing what all the camps bring to this budding field. I have worked with an excellent student on SPMD auto batching for his thesis project and we now have some things to show [2]. This is still a great time to be a machine learning practitioner and endlessly exciting if you care about the intersection between Machine Learning and programming languages.
[2]: https://github.com/FluxML/Hydra.jl
My only request would be for Jeremy to explain “Swift for TensorFlow is the first serious effort I’ve seen to incorporate differentiable programming deep in to the heart of a widely used language that is designed from the ground up for performance.” to me. Is it the “serious” and/or “widely used” subset where the Julia camp is disjoint? =)