A few of those developments are well consistent with what people already knew; it's only a matter of tidying it up into a new or updated framework, and that's what the paper is trying to.
For example. Hockett puts some "hard" barrier between human language and non-human communication. Nowadays we know it's more like a gradient; like, we can agree something like the song of a whale is not language yet, but closer to it than the whimper of a dog, right?
Multimodality (or: how human language uses multiple channels at the same time, not just audio) is also something a bit obvious. Specially for those from cultures where gestures are common; you can convey multiple meanings through the same voice sentence, depending on the gestures and expressions you use.
Challenges outdated textbook narratives that equate language with speech.
Speaking on that: it always makes me roll my eyes when people compare sign languages with dancing bees. That's as silly as comparing voice languages with crickets, for roughly the same reasons.