I love your idea of a narrative about people who live on a boat in the far future. Lots to play with there, thinking about how earth has changed and why people left to other planets. I like the tile system you're thinking of and how this can change with each story beat, lot of ways to deliver this new world you're wanting to show us. I think the style your are going for with the blocky 3D has good potential to fit your theme of a humble yet futuristic simple old earth. Since this is a story heavy game you're making, lean into that as much as possible, how can you tell the story by showing and telling alike? How do the character's actions shape the story and this world that is around them? Really hone in on evocative storytelling, it can be super powerful, especially in your case. Also keep an eye on scope when creating these branching narrative paths, but stick with it because this is a supper cool idea that has a ton of potential! Really looking forward to playing through this mystical tale, good luck with this epic passion project!