still, you shouldn't have your whole game world (if its big) simulated at once. It's ovekill.
Not even NES games did it.
Of course, unless you design really depends on it.... but most don't. Metroid/Megaman/Castlevania doors are a great example of breaking up the world, but if you don't want pauses you could get away with "streaming" the way GTA does it, just load blocks as you're within appropiate distance.