To say UNIX was perfect and needed no improvement would be kinda stupid, the sort of thing Team Amiga would say. No, the question isn't "Are there problems in current UNIX/Linux?" The question is "What is the best way to improve the UNIX implementation in the currently popular Linux/GNU/X systems?"
One way is to discard the base ideas the whole thing rests on and just make it more like Windows, iOS or Mac. (Saying Mac OS to make clear the distinction between the largely ignored UNIX underbelly of OS X and the visible part.) Another way is to evolve it to more closely approach the ideal of the basic ideas. In which case things like Plan 9 are a better lodestar to steer toward and steal ideas from.