Re: Nishikori and Tomic will be the first youngsters to break into the top 10
Tomic has a lot of talent, no doubt, but his commitment to being a true professional is questionable. Success in the juniors does NOT guarantee anything at the pro level. And neither does early tour success. Once the main draw (top 50) players find your weaknesses, word spreads quickly throughout the locker room. Tomic is not known to dig into a tough match all the time, especially in the early rounds of tournaments. He also plays very flat on his forehand which can create spectacular winners but also LOTS of errors.
Nishikori, to my eye, seems destined to hover between 20 and 60 in the world for most of his career. He is incredibly fast and very professional in his consistent effort, but his serve is not very big by tour standards and he lacks the "everything back" determination of a young Lleyton Hewitt or Michael Chang.
Maybe time will prove me wrong about both these players. They are very young after all. But right now I just don't see either of them ever challenging for Grand Slam titles.