How about a mod that covers the era from the 1460s to 1620s, the era of discovery, exploration, and settlement?
This is an era that is largely neglected in all genres despite being a period of high adventure, survival, exploration, discovery, and expansion. Along with major historic events.
The game could start at a point where major European powers are sending out discovery missions to the oceans, like the missions that Henry the Navigator organized. This could be followed by discovery, trade, and expansion of these powers to the lands across the oceans.
The player can get involved in this grand scheme of events, serving any power while also making himself/herself prosper. Discovery, survival, warfare, privateering/piracy, and politics can be mixed together.