From the announcement:
What seems to work best is to keep the forces small and focused like in DeepWars, with lots of character for each troop type. We will stick to the starter sets with 5 models per box but we will try to have all of them metal this time. The initial forces will be Fortune Hunters and Dark Mariners, with the Axibalan empire coming next as a stretch goal, then Draconid Legion. Other mercenary forces will be unlocked after that along with the supplements for different regions of the Underlands. The starting date would be after the DeepWars rewards all ship, so probably late August.