Give Kyrgios time to mature, of course he has it in him to be a slam winner. His talents are immense. His mentality definitely needs work but remember his age. The massive edge he has over others is his inability to be phased by the big occasion. That is almost something you are born with, an innate personality trait. To not crap yourself under pressure. If he works hard physically and recognises that he needs to control his emotions on court, he will go far. Because he already has the self belief. I think he will win a slam at some stage. Its easier to say he wont because chances of winning a slam are remote for anyone in general. So saying he wont is not saying much at all.