This popped into my head and I really like it. So imagine the further you go south the hotter it gets exponentially. Players would expect something similar but I'm saying it gets so hot you end up with shallow water, stretches of barren seabed, lava lakes which would require special ships to sail.
While if you head north it eventually just turns to solid ice requiring ice breakers or eventually vechicles that drive on the ice to go further north where you would maybe run into a solid ice wall (you could possibly bore a tunnel through with a vehicle with a front mounted drill) There could be rare resources in both places requiring visits to both for endgame tech.
I was sitting back mulling over the idea but I kept expanding on it. I imagine driving a truck over the solid ice carrying a full load of rare ore we've mined to our ship that is waiting where the ice begins. -Or sailing on seas of lava in an obsidian plated ship fighting the temperatures.
I would have these north and south lands start very very very far out in each direction, nobody should accidentally find it, you'd have to really journey north or south.
This obviously isn't entirely realistic, but I think it'd be a mind blow and fit the game nice while giving more use for some of the tech available and providing more potential machinery.
Islands and animals surviving on them would be terrifying, but once you reach the "end" there would only be ash or ice mounds scattered around showing that nothing survives that far out. Progressing further than that would lead to just a wall of extremely hard ice (not sure what the lava equivalent could be.)
Inside the ice could be veins of rare ores that possibly don't stack requiring you to haul it back on a large vehicle.
..Or maybe even the ore needs to be forged on the side with the lava, it'd go from lava lakes to strips of obsidian land with tunnels leading to the planets core where you'd forge the ore.
You'd be required to make both trips to reap the rewards.
I've been fleshing this idea out as I'm writing it so I apologize for jumping all over the place.