This is a good news and another opportunity for Ancelotti to add the world cup to what he has achieved so far as a successful coach.
Ancelotti never won a world cup. It is the chance to win a world cup and complete his career with the most prestigious trophy in football. However, he is already one of the most successful coach in history even if he may fail to win a world cup title with Brazil.
I believe that Ancelotti will transform the team and bring out the best of them, because Brazil has great young players doing pretty good in their various clubs. I am happy that the Brazilian National team will be lively again.
Since Ancelotti never succeed with a national team, I'm not really sure that Ancelotti can instantly improve the performance of Brazilian team. But I believe Ancelotti has the ability to change Brazilian team, he has proven his ability by winning varied titles.