So, I've been toying with some ideas about the hardcore quest-type maps. There's been 'rebuild the world' with Agrarian Skies, and 'survive the desert (hot and cold versions)' with Crash Landing and Blast Off. I was sort of thinking about an ocean variant - a world where the seas have risen to completely submerge the land. Thing is, I'd want to see actual biomes in it, with real terrain (yes, things like flowers, tall grass, and vines would wash away, but that's where quest rewards could come in.)
The first problem I see is that - while a super-flat map can be made with water as deep as you want and a single biome - I need to find a way to replace the air blocks above ground on a 'normal' map with water source blocks, such that extended travel wouldn't result in a sudden waterfall. (The possibility of a sudden wall of ice rising from a tundra biome just occurred to me, but I find this idea amusing enough to leave as a potential 'feature'.)
Mods that might be useful