Not that Modric can motivate young players or he will provide them with experience. He is not new in the club and he has being doing it which these young players already know his potential because whenever the game is tough in the second half and Real Madrid needs goal, he substitutes Modric and brings out Kross from the pitch.
Modric can help young players or newcomers in Real Madrid very well. I imagine that Modric can play that role similarly to Ibrahimovic did in AC Milan some years ago. Ibra came to AC Milan when they struggled to build up a strong team with many young players. With Ibrahimovic, their young players got good lessons, motivation from him, and became stronger mentally to win Scudetto two seasons later. Compare AC Milan and Real Madrid - that just won La Liga and Champions League last season - is not too fitted but Modric can do that role well.
Modric has always being a game changer when he handles the midfield because that is what he is good at so I am not surprised that Real Madrid signed a new contract with him since Kross is gone. This is why Ancelotti is not talking about replacing Kross.
Modric can play 15 to 30 minutes and make good contributions and he shown that he has no big problem to stay on bench and play matches as an alternative player.