There was a lot of noise about this. But if you read the blog post carefully, Jeremy only said the Swift thing is very interesting and we will keep close eye on it and consider use it in the course.
I was in the live version of the most recent course. The last two weeks were guest lectured by Chris Lattner on Swift for TensorFlow.
Edit: this appears to be a link to Part 1 which was released in January (and is excellent). The s4tf portion was in part 2 which should be released publicly sometime this month.
"The combination of Python, PyTorch, and fastai is working really well for us, and for our community. We have many ongoing projects using fastai for PyTorch [...] This stack will remain the main focus of our teaching and development.
It is very early days for Swift for TensorFlow. We definitely don’t recommend anyone tries to switch all their deep learning projects [...]"
So basically, nothing promised for v4.