My guess is that Jose and the core team are both personally interested in the big wave of ML stuff we've been experiencing recently and also want to demonstrate that Elixir is a viable platform for doing this work to teams which have adopted Elixir and are interested in ML but don't want to add a bunch of Python into their codebase.
I would also guess that Elixir led to some crazy things they didn’t even imagine possible with web, like phoenixs live view [1]. Even if they don’t have explicit ideas of how it will impact ML, it’ll be really interesting to try.
