I'm not in the loop here, most of the games I've installed from steam are in the 1GB to 20GB range, with a few outliers up to 80GB (I guess). IIRC some recent AAA games are in the 200GB range due to HQ textures. So I think 400GB games are realistic within the next decade. But honestly, it was just a random example. Just s/single 400GB game/400GB of whatever/ ;-)