I think that chance has passed him by - asking a 9 slammer to double his count from 28 on is a big ask. For me, his problem has been not having the "final day" mode that Fed (and then Nadal too)managed to develop. That anticipation you felt as you waited to see how much they could elevate their play in the final....then inevitably you were blown away with some outrageous stuff. Nole's game is perhaps the most solid day in/day out game ever....he is like a metronome. That is highly laudable. But the the reason he hasn't amassed more slams, imo, is that he doesn't really have another level, and too often he has been rocked off kilter in a big match or final by a guy who does.
He has become much better than I thought he could be though, fair play. It's hard to dish out future slams on a forum, when things in the tennis world can change fast. All we need to do though is look at the names he has already surpassed....he is entering the tier 2 ubergreat category. He is unlikley to make it as far up the mountain as Fed, but it's a heck of an achievement.