Im not sure we'll see a dominant top 4 like we have now in a long time. Ferrer is the best of the rest we have currently but he's like 30 now and he's miles away from touching the top 4.
I dont see raonic/dolgopolov ever being a top 5 player,Tomic has potential and i like that kid Goffin's game too. I could see them maybe being strong contenders but nothing as consistantly dominant as our current gen.
I just hope we get some new talent break through because when federer retires and nadal/murray/djok all start getting older, the new "top" players will seem like a step backwards.
To be a tennis pro, you have to get good at handling players balls.