The team believes that RIFT has two types of players: ones who want to enjoy the story and ones who just want to level already. Nightmare Tide is built with both in mind, allowing people to delve into the story as much or as little as desired. However, Trion's Bill Fisher told me at this year's PAX Prime that the story is so good this time around that he's had a hard time doing the MMO gamer thing of ignoring the quest text.
At one point, players will encounter the birthing of a clutch of Skelf eggs. Skelf are humanoid sea creatures (some are like sharks while others share similarities to angler fish) who tend to kill the weakest member of a clutch. However, player intervention will save a poor Skelf baby who will then follow that player around and become a key part of the expansion tale.