I think, maybe, the stronger argument is that the area of Generative Programming (which covers just about anything that generates another program) itself is too broad to properly address in a semester course. This course is particularly focused on metaprogramming, where ML has less relevance. This is to be expected, given the instructor.

It's fairly common practice for the title of the course to be far more broad than the topic. See: "Theory of Computing" courses which spend all their time on complexity classes and never mention automata, or graph theory courses which don't ever mention monadic second order logic or spectral graph theory. Decisions have to be made about what to keep and what to cut, at some point.

I spend a lot of time reading papers at the intersection of ML & PL, so I'm a bit sad, personally, but I don't think it's fair to say the course is out of date. Rather, this is just a sign of the known world getting bigger.