Well, unfortunately, Gackt has stated (very firmly) that he will a) never get married again, and b) never have children. *sniffle* It makes me very sad, but I suppose there's nothing we can do about it.
And also, think about some of the things that he has said. Even though he knows what it feels like to have your life dictated as a child, and he didn't enjoy it, even now he is still kind of a control freak (no offence to Gackt).
And then, even if he would be an excellent father, doesn't it seem like he wouldn't be able to see it? He, sadly, does not have a very high opinion of himself. And so I think that he would always be questioning his parenting abilities, and that would be a depressing situation.