Janowicz is the first young player I've seen in a while that I think capable of cracking into the top 10 and perhaps the top 5. He has all the shots and good movement for a guy 6'8". A bigger serve than Del Potro, maybe as big as Isner and Raonic, and a big forehand. Drop shots like a demon, maybe too much, lobs. Backhand needs to be stronger, especially down the line. He seems to have a fairly strong mentality, but will it be consistent enough? Also, the only thing against the big, big guys is trouble staying healthy. I think Tomic is a bit overrated, but maybe he'll develop. Dimitrov, hmm, he has shown flashes, but he can't seem to break through against the top guys. Sisjling is good on hard indoors, and faster surfaces. I don't think he'll produce on the slower surfaces that exist everywhere now, and he is in his prime years already.
I think we have to wait about 3 or 4 more years and see if anyone else rises. I don't see many other possibilities at the moment.