Real Madrid playmaker, Lukas Modric is an experienced player that have lifted significant and memorable titles with Real Madrid, his respects is earned through years of commitment to Los Blancos at Santiago Bernabeu. Carlo Ancelotti resting the Croatia international is simply because there's replacement for him and the coach is eager to watched these young talents play good football without the guidance of these senior players. Though Toni Kroos is been effective in games, but still have backup, weak bones doesn't generate vital results for the team.
There shouldn't be any debate about him because in the end he will be replaced by another player, and a team that can make changes to its players at the right time will be able to keep the team stable in its performance, and I think Luca Modrid won't have a problem with that either because he certainly realizes that his time at Real Madrid will not be long so the team will slowly start to replace him with younger players.
Real Madrid has been quite successful this season with their young players, at least that's what has been seen so far, and next season it is very possible that they will be even stronger because the players are getting more compact and they just need to find a replacement for Ancelotti who can make this team even better.