There is a little snippet from the 8th Edition rulebooks new fluff section that includes a passage mentioning a Nautican type army. Quote from p.24 is:
554 FROM BENEATH THE WAVES
A Dark Elf Corsair fleet is dragged beneath the waves by an onslaught of submersible craft that appear to be half ship and half kraken. Only one of the Druchii corsairs survives and his tales of needle fanged warriors from the depths are dismissed as salt-madness.
Why take the time to include such a race into the historical narrative if you are not going to flesh out the story somehow? Yes they have Chaos Dwarfs etc who are part of that same narrative and there hasnt been an official book to support them. But the unofficial army books for armies lie Chaos Dwarfs, Kislev and Cathay have been around for a while now and are well known. The Chaos Dwarf one is now widely accepted at tournaments internationally as a legitimate army book. Consequently, there is no real need for GW to look at making an official one there.
With Kislev and Cathay there is an opportunity to make money from figures (as some are available for Kislev, or at least used to be). But both of these nations are difficult to insert into the wider narrative because of their geographical location in the Warhammer world. Plus the have the baggage of several years of fan based literature to go with them, and the ability to have figures made for them out of existing models.
A Nautican race therefore makes more sense as a new army. Why?
- Geographically they would have contact with every other WHFB race allowing them greater capacity to be woven into the existing narrative.
- Starting with a fresh race would allow GW to generate a new storyline without any existing fan fluff behind it. This gives them a clean sheet and removes any possible backlash in regard to widely accepted fan doctrine about such a race.
- An all new race also removes the ability of gamers to modify existing models to create figures for that race. Hence GW can produce a brand new line of models and make a lot more money out of us.
- An oceanic race is perhaps (other than an avian one) the only missing thread from the Warhammer world. We have all the traditional fantasy elements: Humans, Dwarfs, Elves, Orcs, Beasts, Ogres and Daemons as well as new elements like Skaven.
What would be even better of course would be if they used Sigmars unofficial Nautican race as the basis for any fishman type army book.