Which team is capable of displacing Australia

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I am just wondering which team is capable of taking the place of Australia as the number one team in the world and when will it happen. Australia seems to be an ageing side now with most of their World Class players in their thirties, so I think they will no longer be the no.1 team in the world, in the not so distant future. South Africans have shown that they dont have the mental toughness to beat Australia. India have come close but havent been able to beat them so far in a series. so which team will it be?