Modrić is supposed to bring the on ball presence in the midfield, whether it means taking a load off of Xabi by playing next to him or instead of him. Same rotation with Ozil. And in the Clasico I'd expect to see the trivote with Modrić aside Xabi and Khedira which would be what would happen had Sahin transfer worked out.
He's still the rotation man, but he is very versatile and incredibly unselfish. He made 2534 successful passes (only Ashley Williams from Swansea had more) and he was one of the cleanest players fouling 0,5 times per game on average, and that's in the toughest league you can get.