you get to choose what biome to spawn in at the start of a world generration and what biome is north south east and west ect
so thats basicly it.
say i wanted wolves and a igloo i could spawn in a snow biome and have forest biomes around me (or whatever biome wolves spawn in)
you could challennge yourself and MAKE a need for exploration like out loads of plains (no trees) all around youput desert bioms all around you for miles and let the rest generatebut as for the seed problem you could select random generation (normal minecraft world generater)and put in the seed
As a mod this would be incredibly useful I think especially for video-makers like myself when we need a particular biome to film in but then again seeds are a great way to spawn in a specific biome but certainly a mod doing this would help greatly!