It's still vague and so we have no real idea what it will be:
Originally Posted by d'Angelo
We’re already at work on the design of Season 6, which is being targeted for a June release. So what’s on the short list of features being worked on? We’re looking at doing some major upgrades on some key parts of the game. Foundry, PvP, and crafting are scheduled to get significant improvements, and there should also be some new features such as a fleet advancement system. We’ll share more details later as Season 6 comes into better focus.