He has already surpassed Nadal on hard. He will never surpass him on clay. Fed's overall records on hard and grass are quite out of reach even for Djoko. Djoko is not even close at USO but I have a little hope Djoko can surpass Fed at AO and he has a better winning % in masters as well.
This thread is about overall slam counts, not pivoted by surface or tournament (AO had 2 completely different surfaces and USO has been slowed down in 2010, while RG was reportedly sped up by the lighter ball). Hard, grass or clay - let Djokovic surpass Nadal first, then we can make projections about him breaking the all-time record.
I doubt Djokovic can reach 11, even with 2 HC slams every year vs. 1 clay slam. It sure looks doable now that Djokovic is at his peak, but players decline fast and it will only take one serious ankle or back injury for Djokovic to lose what gives him the edge, and looking at what he does on court I can clearly see that injury coming.