Glad to see my fears were misplaced about the social behaviors. This will go a long way to bringing lagoons up the same standard as the dinosaurs (and 2 synapsids) in the game (though pterosaurs also lack social behaviors as well, but hopefully in due time, rather this patch or another). I do think this was a major thing that should have been shown earlier considering the nature of the upcoming DLC tied with this update. I imagine this may have been harder to implement earlier, considering the nature of the marine animals (and pterosaurs), but better late then never.
Edit: Agree with the above poster that things like breaching, etc would also be very welcome additions, and help expand their existing (limited) behavior.
Since this was a major addition being kept secret until now (unless the earlier teased Shonisaurus pair was an example of this, but it was best to take it with a grain of salt at the time, and keep expectations leveled), I hope there's more coming for lagoons still, since aside from the major behavior aspect, and a new attraction (the dome), there's still quite a bit that could be improved upon. One major thing is we still need more enclosure customization (like kelp and coral brushes, terrain painting, etc). Both the dinosaurs (and 2 synapsids), and have pterosaurs (aviaries) have loads more customization. The decorations (that came with the Late Cretaceous pack update in last September, nearly a year ago now) were a good start, but there's a limited selection, and it gets rather tedious placing everything for large lagoons, lest they remain barren and sparse. I imagine brushes are probably way more performance friendly too overall then lots of individual decorations all over the place. It's also strange that kelp is still lacking from this game with how highly requested it is, and also when it is always shown at the start of the game, with the Mosasaur swimming through a kelp forest. I mentioned that in my previous post, but I think it bares worth reiterating.
The other thing lacking is that marine animals still have no way to be a threat to any of the guests, compared to the land animals and pterosaurs. I'm not sure how something like that could be implemented short of a new marine tour, or the Nothosaurus being the lone animal able to escape due to its limbs (though I'm doubtful resources would be expended on a lone animal, since it would probably require a new system implemented, akin to raptors climbing fences, plus animations for it on land). None of the other attractions in the game can be interacted with or damaged by any of the animals, so I doubt things like the new underwater viewing dome would be an exception to that.
Edit: I still think new feeder types would be most welcome too. Nearly every marine animal eats from the same exact fish and/or shark feeder. We need more variety for our animals diets. Ammonite, squid, crabs, etc. Actually land carnivores should get some variety too (more prey types, including the new insect feeder). Herbviores have everything beat with the variety they get (though a few more new plant types like Aruacaria, ferns, horsetails, etc wouldn't hurt, especially since those are common Mesozoic plants missing from the game still).