I'd be surprised if it's dead. At least two of the people on the Swift for Tensorflow team were building a deep learning library in Swift before Swift for Tensorflow was a thing. Much of their work is a part of Swift for Tensorflow.
Jeff Dean seems to disagree.
Also, I think it hasn't picked up steam because it just isn't mature enough yet
I suspect it will drift along like the Java TensorFlow wrapper. Useful in some specific circumstances, but unused outside that.
The only people who seem to be saying it will continue are people outside Google. Crucially there's no one within Google saying they use it for internal projects.