Please take a look on this suggestions, especially for the single player, because there are many players without friends , that need to play single.
1. Pirates ship with crew, chest full of goods, treasures.
2. Some kind of base defence system, being attacked by an army of spawned pirates.
3. A single player settlement, where NPCs are acting like settlers (defend, have jobs working on stations,farming)
4. Advance pirate settlements to conquer. Like more pirates, buildings, treasures, animals. Even a strong fort.
5. A black market that sells random rare items like weapons, armors, ship parts.
6. Stranded NPC. Npc with unique abilities that you can find on islands or floating in waters that you can rescue and recruit or simply take them in towns for a good ransom.
7.Mariage. Ability to marry an npc and have kids. The ideea of a loveed one that is waiting you home.
8. Heroes NPC to recruit, people that never die and simply pass out untill you give them healing.
9. ARENA. A place where you can fight with npc/beast, win gold and powerfull items.
10. Diferent start as single player. Like a rich adventurer, pirate, stranded guy....maybe a little story of your life.

Please consider this for a new mods or improved mods.