Yeah, I don't buy the justification versus Julia because of community size either, given most of Swift's community has little to do with data science. The document even says as much, contradicting that rationale, later on.
As someone who uses TF heavily, I would be much more excited about this project if they'd chosen Julia. Swift's tooling isn't great, and I already have a foot in one language with an immature data science ecosystem (Rust).
How is Rust-Julia interop?
I imagine calling Rust from Julia will be much more common than calling Julia from Rust. I know approximately nothing about this, but there are plenty of questions about embedding Julia into C/C++[2][3]. May be similar for Rust.
[0] https://github.com/dyu/ffi-overhead [1] https://github.com/robsmith11/fastfloat [2] https://discourse.julialang.org/t/support-with-embedding-jul... [3] https://discourse.julialang.org/t/api-reference-for-julia-em...