^ This.
In my dreams, DA4 is set around Antiva/Rivain and involves lots of intrigue with Crows, the Felicisima Armarda, and the Qunari with a ship as your base of operations and nautical combat mechanics, sort of like in Assassin's Creed Black Flag.
Totally beat me to it. Damn!
But yeah, a pirate ship could totally work! You have your ports (and maybe even Ports, haha, okay, I slap myself now) in Tevinter, Seheron, Antiva and Rivain, you have intrigue, you have swashbuckling high-seas adventure... what is not to love? Absolutely behind the AC4 as an inspiration in terms of naval mechanics. And, one more important thing - make the ship customizable. I want a captain's cabin covered in swag amassed during my misadventures.
One of the opening quests could be us getting the behemoth of a ship we will use - it would have to be large, if it is to house out entire coterie - by stealing it, for example (most likely from Isabella). Imagine, sneaking around a Tevinter dock under the cover of the night - I can almost smell the seaweed and guano.
Also, going the pirate route would provide unique visuals and atmosphere to the installment, which would definitely set the game apart. It would show us yet another side of Thedas we have yet to see. And there are not that many fantasy pirate/maritime RPGs around. Sure, there are plenty of your standard high-fantasy faux medieval concepts - I have lost count how many times I walked through an elfy forest or a brown rainy countryside across the genre. But ships?The market is there, and it is up for grabs. Dragon Age: Black Flag could work. Within the market, within the genre, and within BioWare's production history.
This damned thing needs to happen.