The addition of a large cave lot that is accessible through the cave entrance. Fully fleshed out and playable conservationist and lifeguard careers. More lore/background surrounding mermaids, more interactions for them. Overhaul of the Island Elementals with a few rituals you can perform with them. Like a fertility ritual (to increase the chance of twins or triplets), immortality ritual (live forever on the islands), a fortune ritual (better luck in social interactions and life events) or even a malicious natural disaster ritual (to evoke earthquakes and storms).
I personally think that they should save Hotels for another pack. With Island Living, the team clearly went with more of a cultural and environmentally conscious approach of the island theme. I've always interpreted Isla Paradiso in the Sims 3 as more of a commercial destination Island, and Sulani as an undiscovered Polynesian hideaway. But that's just personal, I guess - I'd rather see them expand on the features that are already there.
