For example, see "A Computational Model for TensorFlow" https://research.google.com/pubs/pub46196.html
There are tons of interesting things going on in TensorFlow from a programming language perspective. It has optimization at the low level, like CUDA and SIMD back ends via the Eigen library [1] (which is pretty crazy C++ metaprogramming in its own right).
But it also has optimization at the high level / cluster level, e.g. deciding which nodes to put computations on, to minimize data movement across various networks, etc.
It also has multiple front ends. Python is the main one, but IIRC people were developing others (maybe not at Google).
I worked adjacent to the TensorFlow team, and A LOT of people had BOTH ML and PL skills [2]. It's not an either-or thing. It's best when you have the same person with both sets of expertise.
I think a big problem with large parts of the academic PL community is they're not exposed enough to real applications. Difficulty isn't proportional to real-world benefit. It's certainly difficult to invent type systems to statically detect minor problems, but that doesn't mean it's important for creating and maintaining software. (Sorry, had to rant about that.)
Machine learning is a domain rife with programming language problems, but of course it takes a long time to develop that expertise. I'm sure Lattner would be a good person to synthesize knowledge in the different domains.
[1] http://eigen.tuxfamily.org/index.php?title=Main_Page
[2] edit: I should really say ML and distributed computing skills. But most people with distributed computing skills know a decent amount about programming languages; they overlap in MapReduce-type big data frameworks too.