None. There is profoundly little value for Google in having Google serve the mapping for iOS, unless Apple is paying the big dollars (I suppose possible given that Google has started monetizing mapping), though we know in the net exchange Google pays far more to sit as the default search for iOS Safari, having nothing to do with mapping.

I've seen the "mobile wars" bit about Apple dumping Google across the news world and it's a bit bizarre really as no one can state what Google gains from the current situation, but I guess just the glory of being iOS' mapping technology?