But here are more data (not mine):
All-time Open Era Grand Slam wins
Federer's career is 5 years ahead of Novak's. Fed has 252 wins in slams by now, Novak 141. That is 111 more, divided by 5, it's ~22. 4 slams per year, maximum 28 wins. So just by reaching semi in every GS, in 5 years he will surpass him. He does not have to win a single GS to achieve this!
Similarly, Rafa's career is 1year ahead of Novak. The difference is 16 wins. Reaching semi in just 3 slams, and Novak will surpass this.
But, of the top 20 in that list, only Hewitt is from Fed's generation(!!!)
And from the current generation, there are 3 already, 2 of which already surpassed Hewitt!
I don't dispute your data, which I'm sure is from an excellent source.
But in order to truly surpass Federer, I think most would agree that Djokovic needs to, you know, WIN some more majors...
I think it would also be appropriate to look at where Federer was in terms of tennis titles at the age Djokovic currently is, to gauge in some way the likelihood of Djokovic catching up...