I'm giggling to myself a bit that my attempt to draw support for domestics derailed everyone into going to the beach, but I am a supporter of both things so -
I think that beaches/coastal lends itself more to a scenery pack than islands. Yes, there is some overlap with the aquatics pack, but not to an unworkable extent.
For Coastal I would like to see -
Walrus. It's big, obvious and reasonably popular.
Coconut crab. It's weird and different.
Pelican. Not fussy on the species. It's a bird.
If fully aquatic habitat mechanics are introduced, Manatees are very popular.
If fully aquatic mechanics for habitat animals aren't introduced, I would be willing to sacrifice a habitat animal on this pack for multiple aquatic exhibit animals both in the standard sized exhibits (like traditional aquariums) and in the walkthrough exhibits (as walkthrough underwater tunnels with sharks, rays, etc. Swimming around guests), and maybe a new touchpool exhibit/interactive as well.
For scenery. Let's finally get some horizontal wood, and two path options - a nul beach path and a clear when elevated glass path.