I know there's no bet to put like this (maybe in some gambling houses in UK) but I bet Mbapeé will get to the top in the next World Cup.
Only 4 goals to get to the top, if we consider France will play next world cup and get at least at quarter finals (easy achievement), there's 5 matches to score 4 goals, considering he's the penalty taker, and considering France is going to be the seed and face at least one weaker team, the chances are high.
Another last thing to consider, the next world cup will have 48 teams instead of 32, so there's more probablity to have weaker teams and more goals.
No doubt, Mbappe is a player who has already played at the top level of world football and is still quite young, which means that he has a lot of time to improve, develop and achieve great success. In his two appearances for France in the World Cup, he has scored twelve goals and is already sixth on the list of "All time leading goal scorers". Only four more away from Klose's record 16. It is no wonder that the whole world of football is already speaking about a new star of world football - Kylian Mbappe. And it is safe to say that this young man has everything to become the best scorer in World Cup history.